Article

Reduction in horizontal transfer of conjugative plasmid by UV irradiation and low-level chlorination

Authors:
To read the full-text of this research, you can request a copy directly from the authors.

Abstract

The widespread presence of antibiotic resistance genes (ARGs) and antibiotic resistant bacteria (ARB) in the drinking water system facilitates their horizontal gene transfer among microbiota. In this study, the conjugative gene transfer of RP4 plasmid after disinfection including ultraviolet (UV) irradiation and low-level chlorine treatment was investigated. It was found that both UV irradiation and low-level chlorine treatment reduced the conjugative gene transfer frequency. The transfer frequency gradually decreased from 2.75×10-3 to 2.44×10-5 after exposure to UV doses ranging from 5–20 mJ/cm2. With higher UV dose of 50 and 100 mJ/cm2, the transfer frequency was reduced to 1.77×10-6 and 2.44×10-8. The RP4 plasmid transfer frequency was not significantly affected by chlorine treatment at dosages ranging from 0.05–0.2 mg/l, but treatment with 0.3–0.5 mg/l chlorine induced a decrease in conjugative transfer to 4.40×10-5 or below the detection limit. The mechanisms underlying these phenomena were also explored, and the results demonstrated that UV irradiation and chlorine treatment (0.3 and 0.5 mg/l) significantly reduced the viability of bacteria, thereby lowering the conjugative transfer frequency. Although the lower chlorine concentrations tested (0.05–0.2 mg/l) were not sufficient to damage the cells, exposure to these concentrations may still depress the expression of of a flagellar gene (FlgC), an outer membrane porin gene (ompF), and a DNA transport-related gene (TraG). Additionally, fewer pili were scattered on the bacteria after chlorine treatment. These findings are important in assessing and controlling the risk of ARG transfer and dissemination in the drinking water system.

No full-text available

Request Full-text Paper PDF

To read the full-text of this research,
you can request a copy directly from the authors.

... Horizontal gene transfer (HGT) is the most significant driver for ARGs propagation in the environment [12][13][14][15]. Three genetic mechanisms are involved in HGT, such as conjugative transfer with the assistance of mobile genetic elements (MGEs), transduction via bacteriophages, and natural transformation of extracellular DNA through competent bacteria [14,16,17]. ...
... Horizontal gene transfer (HGT) is the most significant driver for ARGs propagation in the environment [12][13][14][15]. Three genetic mechanisms are involved in HGT, such as conjugative transfer with the assistance of mobile genetic elements (MGEs), transduction via bacteriophages, and natural transformation of extracellular DNA through competent bacteria [14,16,17]. Hence, regulating the ARGs and their dissemination through HGT in WWTPs and DWTPs is the uttermost important for public health. ...
... However, the prolongation of the mating period from 6 h to 24 h did not result in a significant increase in transfer efficiency [109]. Lin et al. [14] demonstrated that the transfer frequency was more closely related to the donor concentration after the mating period of 24 h rather than the initial concentration at the start of mating. This phenomenon can be explained by the regrowth of the donor bacteria due to dark repair and photo-reactivation [14]. ...
Article
Full-text available
Extensive application of antibiotics in the last few decades has promoted selective pressure to disseminate antibiotic resistance in the aquatic environment. Antibiotic-resistant genes (ARGs) and bacteria (ARB) were detected in wastewater, effluent from wastewater treatment plants (WWTPs), surface water, and finished water from drinking water treatment plants (DWTPs), and even in tap-water. Hence, the spread of antibiotic resistance has become a threat to public health. Traditional low-pressure UV lamps (LP UV) removed ARGs, but the fluences required to deactivate ARGs were very high. The efficiency of LP UV to diminish ARGs was more strongly correlated with adjacent thymine number rather than amplicon length since cyclobutane pyrimidine dimers (CPDs) are the significant lesions generated due to UVC-caused damage to DNA. Co-exposure of LP UV with other radicals in the UV based advanced oxidation processes (AOPs) exhibited some improvement in reducing concentrations of ARGs, specifically extracellular ARGs (eARGs). However, the exhaustion of radicals by various cellular components, such as cell membrane, cell wall, and cytoplasmic protein, has limited the widespread application of UV based AOPs. In LP UV-based AOPs, DNA damage induced by LP UV was identified as a major mechanism for eliminating ARG transformation. UVC light-emitting diodes (UVC LEDs) are increasingly being investigated for disinfection performances. 265 nm LED has shown better performance in controlling antibiotic resistance than 285 nm. Further researches are required to assess the performances of UVC LEDs and UVC LEDs based AOPs to deactivate ARGs.
... On the other hand, some previous studies suggested that H. pylori may show resistance to some disinfectants. In relation to this, Baker et al (2002) and Lin et al (2016) shown that H. pylori is more resistant to chlorination and ozonization than E. coli. It is well known that the ability of biofilm formation also provides resistance to disinfection applications (18,19). ...
... In relation to this, Baker et al (2002) and Lin et al (2016) shown that H. pylori is more resistant to chlorination and ozonization than E. coli. It is well known that the ability of biofilm formation also provides resistance to disinfection applications (18,19). ...
... Moreover, H. pylori strains were found to be more resistant to chlorination and ozonization than E. coli (18,19). It is well known that E. coli is a coliform bacterium which is defined as a biological indicator for detecting fecal contamination of water samples. ...
... Traditionally, the occurrence of HGT has been proven under laboratory conditions using well-characterized recipient strains and donors with known plasmids (Top et al. 2002;Johnsen and Kroer 2007;Jutkina et al. 2011;Lin et al. 2016;Pasumarthi and Mutnuri 2016). Few studies have introduced strains with known plasmids into soil containing unknown recipients, imitating bioaugmentation (Top et al. 2002;Garbisu et al. 2017). ...
... At the same time, the HGT process in the microbial community may indirectly be described by the quantity of genes enabling horizontal transfer, including FlgC, OmpF, and TraG (Gillings et al. 2008(Gillings et al. , 2015Jechalke et al. 2013;Koczura et al. 2016;Lin et al. 2016;Xu et al. 2019). The FlgC gene encodes a flagellar protein that is needed to build flagella, enabling the movement of donor cells to the recipient cell, which is needed for direct contact and further conjugation. ...
... hydrocarbon-oxidizing bacteria, we estimated the abundance of bacterial catabolic genes encoding enzymes capable of performing this function. The hydrocarbondegrading genes presented in the literature are diverse; for this investigation, we used five genes that cover the majority of hydrocarbon catabolic processes that are driven by bacteria-alkI, alkII, alkIII, GN-PAH, and GP-PAH (Kohno et al. 2002;Ren et al. 2004;Cébron et al. 2008;Jaktaji and Heidari 2013;Lin et al. 2016). The gene copy numbers were estimated, and the results are presented in Table 5. ...
Article
Full-text available
Oil spills are events that frequently lead to petroleum pollution. This pollution may cause stress to microbial communities, which require long adaption periods. Soil petroleum pollution is currently considered one of the most serious environmental problems. In the present work, processes occurring in the bacterial communities of three soil samples with different physicochemical characteristics, artificially polluted with 12% of crude oil, were investigated in 120-day laboratory experiment. It was found that the total petroleum hydrocarbon content did not decrease during this time; however, the proportion of petroleum fractions was altered. Petroleum pollution led to a short-term decrease in the bacterial 16S rRNA gene copy number. On the basis of amplicon sequencing analysis, it was concluded that bacterial community successions were similar in the three soils investigated. Thus, the phyla Actinobacteria and Proteobacteria and candidate TM7 phylum (Saccaribacteria) were predominant with relative abundances ranging from 35 to 58%, 25 to 30%, and 15 to 35% in different samples, respectively. The predominant operational taxonomic units (OTUs) after pollution belonged to the genera Rhodococcus and Mycobacterium, families Nocardioidaceae and Sinobacteraceae, and candidate class ТМ7-3. Genes from the alkIII group encoding monoxygenases were the most abundant compared with other catabolic genes from the alkI, alkII, GN-PAH, and GP-PAH groups, and their copy number significantly increased after pollution. The copy numbers of expressed genes involved in the horizontal transfer of catabolic genes, FlgC, TraG, and OmpF, also increased after pollution by 11–33, 16–63, and 11–71 times, respectively. The bacterial community structure after a high level of petroleum pollution changed because of proliferation of the cells that initially were able to decompose hydrocarbons, and in the second place, because proliferation of the cells that received these catabolic genes through horizontal transfer.
... As a final procedure of drinking water and wastewater treatment plants, disinfection plays a vital role in inactivating various pathogenic microorganisms for sustainable water safety (Cai et al., 2021b(Cai et al., , 2021aLu and Guo, 2021). Among the treatment technologies, chlorine, UV, and their combination (i.e., UV/chlorine) have been widely applied and investigated due to their high disinfection efficiency (Cai et al., 2021b, Guo et al., 2022Lin et al., 2016). However, the emergency of disinfection-associated microbial risks has been recently highlighted because of the induction of resistant viable but non-culturable (VBNC) bacteria and the limited elimination of ARGs by these treatment strategies (Cai et al., 2021b(Cai et al., , 2021aLin et al., 2017). ...
... Guo et al. (2015) reported that low UV doses (≤ 8 mJ/cm 2 ) posed little influence on the conjugation-related HGT process, while low chlorine doses (≤ 50 mg Cl min/L) significantly accelerated the transfer frequency of ARGs by 2-5 fold. Our recent study showed that both UV irradiation and low-level chlorination could reduce the plasmid RP4-mediated conjugative transfer rates (Lin et al., 2016). Subsequently, Zhang et al. (2017) found that disinfection via chlorine, chloramine, and H 2 O 2 at sub-inhibitory concentrations led to the conjugative transfer promotion of multidrug resistance genes. ...
... Generally, the residual chlorine in the supplied drinking water could be quenched after entering the human body. All previous studies have only focused on the instant bacterial responses on HGT of ARGs after disinfection (Guo et al., 2015;Jin et al., 2020;Lin et al., 2016;Zhang et al., 2017;, whereas the subsequent or lagging effect on this process is currently seldom explored. ...
Article
Disinfection is known to greatly alter bacterial characteristics in water, and high horizontal gene transfer (HGT) frequency occurs in eutrophic conditions. Interestingly, these two seemingly irrelevant phenomena were closely linked by a lagging response of the increased conjugation frequency probably via daily water disinfection in this study. Three disinfection methods (UV, chlorine, and UV/chlorine) were selected to investigate the increased frequency of conjugation of ARGs during the stage of continuing culture after disinfection. The results showed that the conjugative transfer frequency was inhibited for all disinfection treatments after 24 h of co-incubation. Unexpectedly, after 3-7 days of co-cultivation, the HGT frequencies were increased by 2.71-5.61-fold and 5.46-13.96-fold in chlorine (30 min) and UV/chlorine (1 min) groups compared to the control, but not in UV-irradiated groups. A neglected lagging response was found for the first time, i.e., oxidative disinfection-induced dormancy promotes conjugative transfer of ARGs. Furthermore, mechanistic insights were gained from (1) membrane permeability, (2) conjugation-regulated system, (3) efflux pump system, and (4) oxidative stress system, suggesting the critical role of enhancing efflux and oxidative stress in the propagation of ARGs. Finally, the known instantaneous effect of oxidation disinfection was compared to address the controversial debate in this research field, proposing that the dormancy level of donor bacteria is the key to evaluating whether it can promote the HGT process. This study has important environmental implications for elucidating the transmission of ARGs after oxidation disinfection.
... Recently, disinfection using different techniques has gone from pathogenic inactivation to the destruction of genes, particularly those that confer bacterial resistance to antibiotics. Disinfection methods include chlorination, UV irradiation, and ozonation, being applied separately or as a combination of both [120,121]. These methods still offer a challenge to researchers in the field. ...
... These methods still offer a challenge to researchers in the field. Some publications have shown that ARB can be effectively removed under laboratory conditions by chlorination or UV [122], and up to 100% if chlorination and UV are combined as a treatment process [56,65]; moreover, the UV irradiation and low-level chlorine treatment reduced the gene transfer frequency by conjugation mechanisms [121], and ARGs genes can also be removed to different extents [56,74,121,123]. The reduction of ARGs (blaVIM, vanA, ampC, and ermB) ranged from 18.7% to up to 99.3% for ozonation. ...
... These methods still offer a challenge to researchers in the field. Some publications have shown that ARB can be effectively removed under laboratory conditions by chlorination or UV [122], and up to 100% if chlorination and UV are combined as a treatment process [56,65]; moreover, the UV irradiation and low-level chlorine treatment reduced the gene transfer frequency by conjugation mechanisms [121], and ARGs genes can also be removed to different extents [56,74,121,123]. The reduction of ARGs (blaVIM, vanA, ampC, and ermB) ranged from 18.7% to up to 99.3% for ozonation. ...
Article
Full-text available
Advances generated in medicine, science, and technology have contributed to a better quality of life in recent years; however, antimicrobial resistance has also benefited from these advances, creating various environmental and health problems. Several determinants may explain the problem of antimicrobial resistance, such as wastewater treatment plants that represent a powerful agent for the promotion of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG), and are an important factor in mitigating the problem. This article focuses on reviewing current technologies for ARB and ARG removal treatments, which include disinfection, constructed wetlands, advanced oxidation processes (AOP), anaerobic, aerobic, or combined treatments, and nanomaterial-based treatments. Some of these technologies are highly intensive, such as AOP; however, other technologies require long treatment times or high doses of oxidizing agents. From this review, it can be concluded that treatment technologies must be significantly enhanced before the environmental and heath problems associated with antimicrobial resistance can be effectively solved. In either case, it is necessary to achieve total removal of bacteria and genes to avoid the possibility of regrowth given by the favorable environmental conditions at treatment plant facilities.
... Although these studies have expanded our understanding on plasmid conjugation, these mating experiments were generally conducted in relatively shorter mating period (4-72 h) (Sørensen et al., 2003;Wang et al., 2015b;Lin et al., 2016;Li et al., 2018) and optimized lab conditions that enabling sufficient cell-to-cell contact between donors and recipients (Musovic et al., 2010;Klumper et al., 2015Klumper et al., , 2016Li et al., 2018). Plasmid conjugation in soil could be affected by many factors including soil bacterial community composition, nutrients competition, and selective forces such as antibiotic and metal Elsas et al., 1990;Fox et al., 2008;Musovic et al., 2014;Klumper et al., 2016). ...
... It was reported that transconjugants appeared immediately after introduction of E. coli C600(RP4) or P. putida BH(RP4) into soil microcosms (Inoue et al., 2009). The donor bacteria were added with a cell ratio at 1:1 to indigenous soil bacteria, which was a relative high level although this ratio had been reported in previous studies (Elsas et al., 1990;Kozdrój, 2008;Lin et al., 2016;Stalder and Top, 2016). We conducted the experiment with a cell ratio at 1:1 for two reasons. ...
... For example, the transfer frequency that estimated via a 48-h filter mating experiment using the same donor strain and plasmid with sewage sludge microbiota ranged from 3 to 50 conjugation events per 100000 cells (Li et al., 2018). Other factors, including antibiotics (Subbiah et al., 2011), nanomaterials (Qiu et al., 2012), metals (Klumper et al., 2016), UV irradiation (Lin et al., 2016), or ionic liquid (Wang et al., 2015a) may also affect the plasmid transfer in soil. Further studies should be conducted to investigate the effect of multiple factors on plasmid transfer and persistence in soil. ...
Article
Full-text available
Plasmid conjugation is one of the dominant mechanisms of horizontal gene transfer, playing a noticeable role in the rapid spread of antibiotic resistance genes (ARGs). Broad host range plasmids are known to transfer to diverse bacteria in extracted soil bacterial communities when evaluated by filter mating incubation. However, the persistence and dissemination of broad range plasmid in natural soil has not been well studied. In this study, Pseudomonas putida with a conjugative antibiotic resistance plasmid RP4 was inoculated into a soil microcosm, the fate and persistence of P. putida and RP4 were monitored by quantitative PCR. The concentrations of P. putida and RP4 both rapidly decreased within 15-day incubation. P. putida then decayed at a significantly lower rate during subsequent incubation, however, no further decay of RP4 was observed, resulting in an elevated RP4/P. putida ratio (up to 10) after 75-day incubation, which implied potential transfer of RP4 to soil microbiota. We further sorted RP4 recipient bacteria from the soil microcosms by fluorescence-activated cell sorting. Spread of RP4 increased during 75-day microcosm operation and was estimated at around 10-4 transconjugants per recipient at the end of incubation. Analysis of 16S rRNA gene sequences of transconjugants showed that host bacteria of RP4 were affiliated to more than 15 phyla, with increased diversity and shift in the composition of host bacteria. Proteobacteria was the most dominant phylum in the transconjugant pools. Transient transfer of RP4 to some host bacteria was observed. These results emphasize the prolonged persistence of P. putida and RP4 in natural soil microcosms, and highlight the potential risks of increased spread potential of plasmid and broader range of host bacteria in disseminating ARGs in soil.
... As a result, UWWTPs have been established to function a key part in the transmission of ARB and ARGs in nature, therefore causing hazards to public health [1]. [33]. Nevertheless, not many new investigations mentioned that chlorination, as a largely utilized disinfection method, might co-select antibiotic resistance. ...
Article
Full-text available
Chlorine is largely used as a disinfectant in the water and wastewater treatment industries through the world despite the fact that is greatly poisonous for human beings. Its toxicity is more extended to generating disinfection by-products during its microorganisms' killing and action on organic matter present in water. More importantly, recent studies proved the potential impacts of disinfection on transmission of antibiotic resistance genes (ARGs), particularly for free-living ARGs in final disinfected effluent of urban waste-water treatment plants. Indeed, Escherichia coli concentration prior to chlo-rination depicted a powerful positive correlation with the extracellular ARGs plenty in the final effluents; however, lower temperature and higher ammo-nium concentration were suggested to relate with intracellular ARGs. Chlo-rination could elevate the plenty of ARGs, therefore, inducing danger of the diffusion of antibiotic resistance in nature. Consequently, chlorine toxicity is more and more proved, which appeals its urgent stopping from using it in the treatment of both water and wastewater. The same conclusion was also obtained at least for UV and UV/H 2 O 2 disinfection. Chemical disinfection should be urgently avoided or at least deeply revised. For removing pathogens and treating water, safe multi-barrier methods, such as distillation and membrane processes, have to be adopted.
... First, it was found that NO exposure caused no significant changes in the cell density (OD 600 ) and cell viability (CCK-8) of the donor/recipient ( Figure S3, p > 0.05), which ruled out the possible contribution of bacteria abundances to the variations in conjugation frequencies. 47 Instead, the intracellular ATP levels were significantly increased by 51.6% in E. coli K12 and 35.3% in E. coli HB101 in the presence of 0.1 mM SNP (p < 0.05, Figure S4), respectively. It is well known that plasmid conjugation is an ATP-consuming process. ...
Article
Full-text available
The dissemination of plasmid-borne antibiotic resistance genes (ARGs) in wastewater is becoming an urgent concern. Previous studies mainly focused on the effects of coexisting contaminants on plasmid conjugation, but ignored the potential contribution of some byproducts inevitably released from wastewater treatment processes. Herein, we demonstrate for the first time that nitric oxide (NO), an intermediate of the wastewater nitrogen cycle, can significantly boost the conjugative transfer of plasmid RP4 from Escherichia coli K12 to different recipients (E. coli HB101, Salmonella typhimurium, and wastewater microbiota). Phenotypic and genotypic tests confirmed that NO-induced promotion was not attributed to the SOS response, a well-recognized driver for horizontal gene transfer. Instead, NO exposure increased the outer membrane permeability of both the donor and recipient by inhibiting the expression of key genes involved in lipopolysaccharide biosynthesis (such as waaJ), thereby lowering the membrane barrier for conjugation. On the other hand, NO exposure not only resulted in the accumulation of intracellular tryptophan but also triggered the deficiency of intracellular methionine, both of which were validated to play key roles in regulating the global regulatory genes (korA, korB, and trbA) of plasmid RP4, activating its encoding transfer apparatus (represented by trfAp and trbBp). Overall, our findings highlighted the risks of NO in spreading ARGs among wastewater microbiota and updated the regulation mechanism of plasmid conjugation.
... For example, after the removal of chlorine susceptible bacteria and immediately after the reduction of the concentration of chlorine, the available niches and nutrients are a plethora for the growth of disinfectant resistance community members. Studies have reported that drinking water chlorination may promote the occurrence of plasmid insertion sequences and integrons involved in the horizontal transfer of ARGs (Shi et al., 2013;Lin et al., 2016;Zhang et al., 2021). ...
Article
Full-text available
Information on the co-occurrence of antibiotic resistance genes (ARGs) and metal resistance genes (MRGs) among bacterial communities in drinking water distribution systems (DWDSs) is scarce. This study characterized ARGs and MRGs in five well-maintained DWDSs in Finland. The studied DWDSs had different raw water sources and treatment methods. Two of the waterworks employed artificially recharged groundwater (ARGW) and used no disinfection in the treatment process. The other three waterworks (two surface and one groundwater source) used UV light and chlorine during the treatment process. Ten bulk water samples (two from each DWDS) were collected, and environmental DNA was extracted and then sequenced using the Illumina HiSeq platform for high-throughput shotgun metagenome sequencing. A total of 430 ARGs were characterized among all samples with the highest diversity of ARGs identified from samples collected from non-disinfected DWDSs. Furthermore, non-disinfected DWDSs contained the highest diversity of bacterial communities. However, samples from DWDSs using disinfectants contained over double the ratio of ARG reads to 16S rRNA gene reads and most of the MRG (namely mercury and arsenic resistance genes). The total reads and types of ARGs conferring genes associated with antibiotic groups namely multidrug resistance, and bacitracin, beta-lactam, and aminoglycoside and mercury resistance genes increased in waterworks treating surface water with disinfection. The findings of this study contribute toward a comprehensive understanding of ARGs and MRGs in DWDSs. The occurrence of bacteria carrying antibiotic or metal resistance genes in drinking water causes direct exposure to people, and thus, more systematic investigation is needed to decipher the potential effect of these resistomes on human health.
... In addition to interventions that reduce the selective pressure of antibiotics or that implement new therapeutic approaches, reducing transmission is also relevant to fight infections. The development of drugs or conditions (as certain wastewater treatments) able to reduce mutagenesis or to inhibit plasmid conjugation may also help in reducing the spread of resistance (Thi et al., 2011;Alam et al., 2016;Lin et al., 2016;Lopatkin et al., 2017;Valencia et al., 2017;Kudo et al., 2019). Besides specific drugs to reduce the dissemination of the genetic elements involved in AR, socioeconomic interventions to break the bridges that allow transmission between individuals and, most importantly (and less addressed), between resistance entities (Hernando-Amado et al., 2019) are needed (Figure 3). ...
Article
Full-text available
Antibiotic resistance is a problem for human health, and consequently, its study had been traditionally focused toward its impact for the success of treating human infections in individual patients (individual health). Nevertheless, antibiotic-resistant bacteria and antibiotic resistance genes are not confined only to the infected patients. It is now generally accepted that the problem goes beyond humans, hospitals, or long-term facility settings and that it should be considered simultaneously in human-connected animals, farms, food, water, and natural ecosystems. In this regard, the health of humans, animals, and local antibiotic-resistance-polluted environments should influence the health of the whole interconnected local ecosystem (One Health). In addition, antibiotic resistance is also a global problem; any resistant microorganism (and its antibiotic resistance genes) could be distributed worldwide. Consequently, antibiotic resistance is a pandemic that requires Global Health solutions. Social norms, imposing individual and group behavior that favor global human health and in accordance with the increasingly collective awareness of the lack of human alienation from nature, will positively influence these solutions. In this regard, the problem of antibiotic resistance should be understood within the framework of socioeconomic and ecological efforts to ensure the sustainability of human development and the associated human-natural ecosystem interactions.
... In addition to interventions that reduce the selective pressure of antibiotics or that implement new therapeutic approaches, reducing transmission is also relevant to fight infections. The development of drugs or conditions (as certain wastewater treatments) able to reduce mutagenesis or to inhibit plasmid conjugation may also help in reducing the spread of resistance (Thi et al., 2011;Alam et al., 2016;Lin et al., 2016;Lopatkin et al., 2017;Valencia et al., 2017;Kudo et al., 2019). Besides specific drugs to reduce the dissemination of the genetic elements involved in AR, socioeconomic interventions to break the bridges that allow transmission between individuals and, most importantly (and less addressed), between resistance entities (Hernando-Amado et al., 2019) are needed (Figure 3). ...
Preprint
Full-text available
Antibiotic resistance is a problem for human health, and consequently, its study had been traditionally focused toward its impact for the success of treating human infections in individual patients (individual health). Nevertheless, antibiotic-resistant bacteria and antibiotic resistance genes are not confined only to the infected patients. It is now generally accepted that the problem goes beyond humans, hospitals, or long-term facility settings and that it should be considered simultaneously in human-connected animals, farms, food, water, and natural ecosystems. In this regard, the health of humans, animals, and local antibiotic-resistance-polluted environments should influence the health of the whole interconnected local ecosystem (one health). In addition, antibiotic resistance is also a global problem; any resistant microorganism (and its antibiotic resistance genes) could be distributed worldwide. Consequently, antibiotic resistance is a pandemic that requires global health solutions. Social norms, imposing individual and group behavior that favor global human health and in accordance with the increasingly collective awareness of the lack of human alienation from nature, will positively influence these solutions. In this regard, the problem of antibiotic resistance should be understood within the framework of socioeconomic and ecological efforts to ensure the sustainability of human development and the associated human-natural ecosystem interactions.
... Disinfection process can inhibit the expression of related transfer genes by reducing the survival rate of donor bacteria, thus removing part of ARGs in water. For example, Lin et al. found that lower residual chlorine inhibited the expression of genes related to extramembrane protein gene and DNA transfer, and reduced ARGs abundance by reducing gene transfer rate [29]. The content of tetG decreased from 7.94 × 10 2 copy/mL to 1.63 × 10 0 copy/mL after disinfection in drinking water plants in the lower reaches of Jiulong River [27]. ...
Article
Full-text available
In recent years, the problem of the pollution of antibiotic resistance genes(ARGs)in water environment is becoming more and more serious. As a new environmental pollutant, people have been paid more attention to the harmfulness of ARGs in drinking water sources. The source of ARGs, pollution status, detection and identification technology and water treatment technology have been systematically reviewed, and the future research directions of ARGs were prospected.
... We observed nearly 200 bacterial cells for each treatment and found about 10% of treated cells had membrane damage. Several previous researchers have found that some chemicals that stimulate conjugative transfer, like chlorination (Guo et al., 2015;Lin et al., 2016) and nanomaterial (Ding et al., 2016;Qiu et al., 2012), can also change the composition and structure of membranes under the observation of TEM. ...
Article
Full-text available
Increasing concentrations of preservatives have been detected in environments due to the overuse and misuse of preservatives in food and personal care products. Recent studies have relied heavily on the toxicity, biodegradability, and fate of preservatives in the environment. However, the biological effects of preservatives on antimicrobial resistance, which poses great threats to public health worldwide, are largely unknown. This study investigated three preservatives for their ability and mechanisms of promoting horizontal transfer of antimicrobial resistance genes (ARGs). The results demonstrated that these preservatives (sodium nitrite, sodium benzoate, and triclocarbon), under daily-use concentrations, led to concentration-dependent increases in conjugative transfer by 1.24–2.63, 6.79–7.05, and 2.17–4.31 folds compared with the control group. Even these three preservatives had different patterns on generating intracellular reactive oxidative species (ROS) and reactive nitrogen species (RNS), all of them could stimulate radical-induced RpoS regulon and SOS response, increase cell membrane permeability, and regulate conjugative transfer-related genes, subsequently promoting horizontal transfer of ARGs. The present results expanded the understanding of biological effects induced by preservatives, and provided mechanistic insight into the preservatives-induced resistance. This study also opens an intriguing question on the roles of emerging contaminants including preservatives in the emerging and spread of ARGs in various environments.
... Disinfection with free chlorine at low doses (0.05-0.2 mg/l) didn't affect the transfer efficiency of RP4 plasmid while high doses (0.3-0.5 mg/l) caused a decrease in conjugative transfer efficiency. Reduced cell viability due to cell damage was the major contribution factor (Lin, Li, Zhang, & Yu, 2016). Chlorination enriched six out of 125 ARGs and one out of 13 MGEs present in a municipal WWTP secondary effluent . ...
Article
Full-text available
Aquatic environments are identified as an ideal setting for acquisition and dissemination of antibiotic resistance, and human exposure to antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in aquatic environments may pose an additional health risk. Quantitative microbial risk assessment (QMRA) has been suggested as a suitable method to evaluate and quantify this health risk. However, information about the exposure to ARB and ARGs in aquatic environments is lacking for many scenarios and dose-response models regarding the ARB infections are not developed yet. This review summarizes the current knowledge regarding the ARB and ARGs in aquatic environments and highlights the challenging questions remaining to be answered to better forecast the health risks caused by ARB and ARGs in water environments. The questions include what are the missing information needed to quantify the human health risks caused by exposing to ARB and ARGs in aquatic environments? what are the suitable markers to evaluate the ARB/ARGs contamination in aquatic environments? how frequently do the ARG selection and propagation occur in aquatic environments? and are there any unknown hot spots? Studies on the above topics will contribute to better management of antibiotic resistance dissemination in water environments and its risks on human health.
... UV can directly damage ARGs and inactivate ARB (McKinney and Pruden 2012). Moreover, UV can limit the spread of ARGs by reducing the horizontal transfer of conjugative plasmid (Lin et al. 2016) and sensitising Pseudomonas aeruginosa PAO1 to multiple antibiotics (Zhao et al. 2018). UV disinfection was confirmed to reduce the absolute abundance, but increase the relative abundance of some ARGs (Guo et al. 2013). ...
Article
Full-text available
Ultraviolet (UV) disinfection is now widely implemented in wastewater treatment plants (WWTPs) worldwide, but its effect on antibiotic resistome of the surviving bacteria remains unclear. In this study, we employed high-throughput sequencing-based metagenomic and metatranscriptomic approaches to comprehensively elucidate the effects of UV disinfection on the shifts of bacterial community and antibiotic resistance genes (ARGs) on both DNA and mRNA levels in one WWTP. Metagenomic analyses revealed an insignificant change in the bacterial community after UV disinfection, while metatranscriptomic analyses showed that UV disinfection significantly changed the abundance of 13.79% of phyla and 10.32% of genera. In total, 38 ARG-like open reading frames (ORFs) and 327 ARG-like transcripts were identified in the DNA and RNA samples, respectively. The relative abundances of the total ARGs, each ARG type, and each ARG subtype also varied after UV disinfection. Additionally, UV disinfection significantly reduced the expression of total ARGs from 49.40 transcripts per kilobase of exon model per million mapped reads (TPM) to 47.62 TPM, and significantly changed the expression of 10.75% of ARG subtypes in wastewater (p < 0.05). Notably, the significant increase in the expression and obvious increase in the relative abundance of macrolide-lincosamide-streptogramin B (MLSB) resistance genes revealed that UV disinfection increases the potential health risk of MLSB resistance genes in wastewater. Moreover, potential host analyses of ARGs revealed the different preferences of antibiotic resistant bacteria (ARB) to ARGs. This study may shed new light on the underlying mechanism of the UV disinfection effect on antibiotic resistance.
... Conjugative transfer has been extensively recognized to occur both in natural microbial communities and in the lab setting (Bellanger et al., 2014), so conjugative transfer may be particularly important in disseminating ARGs in drinking water systems via plasmid. (Thomas and Nielsen, 2005;Burch et al., 2014;Lin et al., 2016). ...
Article
The widespread emergence of antibiotic resistance genes (ARGs) in drinking water systems endangers human health, and may be exacerbated by their horizontal gene transfer (HGT) among microbiota. In our previous study, Quorum sensing (QS) molecules produced by bacteria from biological activated carbon (BAC) biofilms were demonstrated to influence the transfer efficiency of a model conjugative plasmid, here RP4. In this study, we further explored the effect and mechanism of QS on conjugation transfer. The results revealed that Acyl-homoserine lactones producing (AHL-producing) bacteria isolated from BAC biofilm play a role in the propagation of ARGs. We selected several quorum sensing inhibitors (QSIs) to study their effects on AHL-producing bacteria, including the formation of biofilm and the regulating effect on conjugation transfer. In addition, the possible molecular mechanisms for AHLs that promote conjugative transfer were attributable to enhancing the mRNA expression, which involved altered expressions of conjugation-related genes. We also found that QSIs could inhibit conjugative transfer by downregulating the conjugation-relevant genes. We believe that this is the first insightful exploration of the mechanism by which AHLs will facilitate and QSIs will inhibit the conjugative transfer of ARGs. These results provide creative insight into ARG pollution control that involves blocking QS during BAC treatment in drinking water systems.
... At the microbial level, drugs used as additives in animal feed capable of inhibiting plasmid conjugation have been proposed 125 . Additionally, certain water treatments may reduce plasmid conjugation 126 , which might be involved in AMR transmission in water bodies 127 , particularly in the presence of low concentrations of antibiotics 128 . ...
Article
Full-text available
Several interconnected human, animal and environmental habitats can contribute to the emergence, evolution and spread of antibiotic resistance, and the health of these contiguous habitats (the focus of the One Health approach) may represent a risk to human health. Additionally, the expansion of resistant clones and antibiotic resistance determinants among human-associated, animal-associated and environmental microbiomes have the potential to alter bacterial population genetics at local and global levels, thereby modifying the structure, and eventually the productivity, of microbiomes where antibiotic-resistant bacteria can expand. Conversely, any change in these habitats (including pollution by antibiotics or by antibiotic-resistant organisms) may influence the structures of their associated bacterial populations, which might affect the spread of antibiotic resistance to, and among, the above-mentioned microbiomes. Besides local transmission among connected habitats—the focus of studies under the One Health concept—the transmission of resistant microorganisms might occur on a broader (even worldwide) scale, requiring coordinated Global Health actions. This Review provides updated information on the elements involved in the evolution and spread of antibiotic resistance at local and global levels, and proposes studies to be performed and strategies to be followed that may help reduce the burden of antibiotic resistance as well as its impact on human and planetary health. This Perspective discusses the emergence and connectedness of antimicrobial resistance across One Health and Global Health levels, as well as potential strategies for mitigating the burden of such resistance in human and environmental health.
... This suggests that drinking water treatment processes are unable to completely remove ARBs and ARGs from water. Furthermore, intact fragments of DNA may confer resistance to downstream bacteria by horizontal gene transfer, and injured ARB can be fully re-activated and retain their resistance [4][5][6]. Horizontal gene transfers consists of three mechanisms: (1) conjugation, which requires contact between cells via cell surfaces or adhesion through which DNA is then transferred, (2) transformation, which is the uptake of naked fragments of extracellular DNA, and (3) transduction, which requires bacteriophage to transfer the DNA. These mechanisms allow resistance to spread between non-pathogenic bacteria and pathogenic or potentially pathogenic bacteria, extending the resistance even further [6,7]. ...
Article
Full-text available
This study determined the effectiveness of chlorine, UV and combination of UV/chlorine in inactivating antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG), as well as potential repair of these bacteria following disinfection processes in drinking water. Previous studies have assessed the efficacy of UV disinfection in inactivating ARBs, however, most of these studies have focused on wastewater treatment applications. The use of chlorine and UV disinfection at typical drinking water industry doses was found to not completely eliminate the resistance genes. Using 30 mg/min/L of chlorine, the inactivation of tet(A), bla- TEM1 , sul1, mph(A) was 1.7-log, while a UV fluence of 200 mJ/cm 2 only resulted in a reduction of up to 1.2-log of these genes. This suggests that these genes can continue to be present in distribution systems even following disinfection. On the other hand, the application of sequential UV disinfection followed by chlorination significantly reduced the ARGs and had synergistic effects compared to single disinfectant use, with a resulting synergy in the inactivation achieved (log units) ranging between 0.01 and 0.62-log across the tested ARGs . The ARBs also demonstrated the potential for re-growth following chlorination up to 5 mg/L and UV disinfection of up to 10 mJ/cm 2 under the conditions of this study.
... The effectiveness of UV technology to control ARGs remains a challenge. In recent years, researchers have been investigating a combination of UV technology with other oxidation processes to achieve efficient control of ARGs and HGT (Lin et al., 2016;Pang et al., 2016;Sharma et al., 2016;Wang et al., 2017c;Michael-Kordatou et al., 2018;He et al., 2019;Hu et al., 2019b;Yang et al., 2019). This review focuses on the recent investigations on the combination of UV with oxidants, which include chlorine, hydrogen peroxide, and photocatalysts (i.e., to create advanced oxidation processes (AOPs)). ...
Article
Antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have been recognized as one of the biggest public health issues of the 21st century. Both ARB and ARGs have been determined in water after treatment with conventional disinfectants. Ultraviolet (UV) technology has been seen growth in application to disinfect the water. However, UV method alone is not adequate to degrade ARGs in water. Researchers are investigating the combination of UV with other oxidants (chlorine, hydrogen peroxide (H2O2), peroxymonosulfate (PMS), and photocatalysts) to harness the high reactivity of produced reactive species (Cl·, ClO·, Cl2·−, ·OH, and SO4·−) in such processes with constituents of cell (e.g., deoxyribonucleic acid (DNA) and its components) in order to increase the degradation efficiency of ARGs. This paper briefly reviews the current status of different UV-based treatments (UV/chlorination, UV/H2O2, UV/PMS, and UV-photocatalysis) to degrade ARGs and to control horizontal gene transfer (HGT) in water. The review also provides discussion on the mechanism of degradation of ARGs and application of q-PCR and gel electrophoresis to obtain insights of the fate of ARGs during UV-based treatment processes.
... plasmid may decrease with increasing UV dose, contributing to a decrease in the frequency of conjugative transfer ( Lin et al., 2016). As far as the authors are aware, there are few reports so far on the effects of UV and ozone on the ARGs in drinking water and the recovery of ARB after treatment, which need to be further explored in the future. ...
Article
Antibiotic resistance in aquatic environment has become an important pollution problem worldwide. In recent years, much attention was paid to antibiotic resistance in urban drinking water systems due to its close relationship with the biosafety of drinking water. This review was focused on the mechanisms of antibiotic resistance, as well as the presence, dissemination and removal of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the urban drinking water system. First, the presence of ARB and ARGs in the drinking water source was discussed. The variation of concentration of ARGs and ARB during coagulation, sedimentation and filtration process were provided subsequently, in which filtration was proved to be a promising technology to remove ARGs. However, biological activated carbon (BAC) process and drinking water distribution systems (DWDSs) could be incubators which promote the antibiotic resistance, due to the enrichment of ARGs and ARB in the biofilms attached to the active carbon and pipe wall. Besides, as for disinfection process, mechanisms of the inactivation of ARB and the promotion of conjugative transfer of ARGs under chlorine, ozone and UV disinfection were described in detail. Here we provide some theoretical support for future researches which aim at antibiotic resistance controlling in drinking water. © 2019, Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature.
... Chlorine dose: more than 30 mg/L Over 90% removal (Oh et al., 2014) FlgC Ã , ompF Ã FlgC, ompF, TraG, plasmid RP4 UV irradiation:5-100 mJ/cm 2 4.23-7.04 logs reduction (Lin, Li, Zhang, & Yu 2016) sulI, tetG, intI1 UV irradiation: 12477 mJ/cm 2 2.48-2.74 logs reduction mecA, vanA, tetA, ampC ...
Article
Full-text available
It is becoming clear that the wastewater treatment plants (WWTPs) is a key repository for antibiotic resistance genes (ARGs), and WWTPs also represent an important node for limiting ARGs spreading via altering the magnitude and distribution of ARGs in environment. This review provides an overview of the ARGs degradation performance both in sewage sludge and wastewater in WWTPs. The ARGs reduction behaviors during sludge treatment processes including anaerobic digestion (AD), composting, aerobic digestion, bio-drying and air-drying were reviewed, and parameters affecting ARGs reducing efficiency and the probable mechanisms were concluded. In particular, pretreatment approaches such as microwave, thermal hydrolysis and ozone before sludge AD are found to provide the extra benefits for ARGs removal. Additionally, ARGs fates and reduction mechanisms during sewage biological treatments such as anaerobic, aerobic, anaerobic combined with aerobic process and physical-chemical treatment including coagulation, advanced oxidation and disinfection processes were appraised. Furthermore, problems or doubts of previous study are proposed, and some in-depth mechanism researches are anticipated to elucidate the ARGs decay in sewage and sludge treatment process. This can help further enhance the ARGs removal efficiency in WWTPs.
... Exposure to free chlorine not only increases cells' tolerance to chlorine (Shi et al., 2013), but may also select for antibiotic resistance (Huang et al., 2011). The effects of chlorine on horizontal gene transfer of ARGs can be complicated: chlorine may promote ARG transfer by improving cell permeability , but it may also lower conjugation frequency by causing a decreased expression of proteins involved in conjugation (Lin et al., 2016). The decrease in certain ARG concentrations by Chlorox and Virkon™ treatment as compared to the control may be caused by oxidation of free-floating DNA in swine slurry (Zhang et al., 2019), which would otherwise be taken up by cells through transformation (Zhang et al., 2013b). ...
Article
Manure storage facilities are critical control points to reduce antibiotic resistance genes (ARGs) in swine manure slurry before the slurry is land applied. However, little is known about how exogenous chemicals entering the manure storage facilities may affect the fate of ARGs. The objective of this study was to analyze the impact of six commonly used pit additives and four facility disinfectants on the concentration of ARGs in swine manure slurry. Bench scale reactors, each containing approximately 50 L of liquid swine manure, were dosed with additives or disinfectants and were sampled for 40 days. Seven antibiotic resistance genes along with the intI1 gene and the 16S rRNA gene were monitored. Out of the six additives tested, Sludge Away significantly reduced the time-averaged absolute abundance of erm(C), erm(F), tet(Q), and the 16S rRNA gene as compared to the no additive control. Out of the four disinfectants tested, Tek-Trol significantly reduced the time-averaged absolute abundance of erm(B), erm(C), erm(F), intI1, tet(Q), and tet(X) than did the no-disinfectant control. According to Spearman's rank correlation, three genes erm(F), tet(Q), and tet(X) showed a strong to perfectly positive correlation and the two genes erm(B) and tet(O) showed a moderate to strong correlation in both the additive and disinfectant tests. Overall, the disinfectants were more effective in controlling the absolute abundance of ARGs than were the pit additives.
... Moreover, extensive studies reported that pollutants (e.g., triclosan, carbamazepine, heavy metals) could facilitate HGT of ARGs via inducing oxidative stress, damaging bacterial cell membrane, triggering SOS response, and enhancing expression of genes involved in mating pair formation, DNA transfer and replication Wang et al., 2019;Wang et al., 2020b). However, recent studies also found that several pollutants such as chlorine, 2,4-dichloroaniline, free nitrous acid, and polycyclic aromatic hydrocarbons could inhibit HGT via inhibiting growth of donor and recipient strains, reducing formation of pili, and enhancing formation of complexes associated with plasmids and pollutants (Lin et al., 2016;Jiao et al., 2017;Wang et al., 2017;Hu et al., 2019;Huang et al., 2019). PA is a heterogeneous chemical mixture whose composition depends on its feedstock and preparation conditions (Ghidotti et al., 2017;Lu et al., 2019), showing powerful antimicrobial activity (Chen et al., 2010;Hou et al., 2018;Li et al., 2019b) and great potential in complexation with heavy metals (Chen et al., 2010;Liu et al., 2018b;Li et al., 2019b). ...
Article
Full-text available
Strategies to mitigate the spread of antibiotic resistance genes (ARGs) in soils are urgently needed. Therefore, a pristine pyroligneous acid (PA) from pyrolyzing blended woody waste at 450 • C and its three fractions distilled at 98, 130, and 220 • C (F1, F2, and F3) were used to evaluate their feasibility of reducing ARGs in soil. Application of PA, F2, and F3 effectively decreased the relative ARG abundance by 22.4-75.4% and 39.7-66.7% in the rhizosphere and bulk soil relative to control, respectively, and the removal efficiency followed an order of F3 > PA > F2. Contrarily, F1 increased the abundance of ARGs. The decreased abundance of two mobile genetic elements and impaired conjugative transfer of RP4 plasmid in the presence of PA, F2 and F3 demonstrated that the weakened horizontal gene transfer (HGT) contributed to the reduced ARG level. Variation partitioning analysis and structural equation models confirmed that ARG reduction was primarily driven by the weakened HGT, followed by the decreased co-selection of heavy metals and shifted bacterial community (e.g., reduced potential host bacteria of ARGs). Our findings provide practical and technical support for developing PA-based technology in remediating ARG-contaminated soil to ensure food safety and protect human health.
... For example, after the removal of chlorine susceptible bacteria and immediately after the reduction of the concentration of chlorine, the available niches and nutrients are a plethora for the growth of disinfectant resistance community members. Studies have reported that drinking water chlorination may promote the occurrence of plasmid insertion sequences and integrons involved in the horizontal transfer of ARGs (Shi et al., 2013;Lin et al., 2016;Zhang et al., 2021). ...
... Initially, all containers were sterilized at 121°C for 15 min and placed into an oven for drying prior to performing experiment. LB nutrient agar was dissolved and sterilized with the addition of TC, kanamycin, and ampicillin at their individual concentrations of 50, 60, and 80 mg/L, which were set according to our recent study (Lin et al., 2016). Afterwards, it was poured into the plate for solidification and preservation for plate culturing of bacteria. ...
Article
The emergence of antibiotics and their corresponding antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have posed great challenges to the public health. The paper demonstrates the removal of co-existing tetracycline (TC), its resistant Escherichia coli (E. coli), and ARGs (tetA and tetR) in a mixed system by applying ferrate(VI) (FeVIO4²⁻, Fe(VI)) at pH 7.0. TC was efficiently degraded by Fe(VI), and the rapid inactivation of the resistant E. coli was found with the complete loss of culturability. The results of flow cytometry suggested that the damage of membrane integrity and respiratory activity were highly correlated with the Fe(VI) dosages. Moreover, high-dose Fe(VI) eliminates 6 log10 viable but non-culturable (VBNC) cells and even breaks the cells into fragments. ARGs in extracellular form (e-ARGs) exhibited a high sensitivity of 4.44 log10 removal to Fe(VI). Comparatively, no removal of intracellular ARGs (i-ARGs) was observed due to the multi-protection of cellular structure and rapid decay of Fe(VI). The oxidized products of TC were assessed to be less toxic than the parent compound. Overall, this study demonstrated the superior efficiency and great promise of Fe(VI) on simultaneous removal of antibiotics and their related ARB and ARGs in water.
... To minimize the differences caused by different DNA manipulation efficiencies and background bacterial abundance, the 16S rRNA gene was used as an internal control for data normalization. The relative abundances of ARGs were calculated using the 2 −∆Ct method (Lin et al., 2016), where ∆C t = C t for target gene, − C t for 16S rRNA gene. ...
Article
Full-text available
Tetracycline (TC) and tetracycline resistance genes (TRGs) in plant edible tissues pose a potential risk to the environment and then to human health. This study used a pot experiment to investigate the effects of different remediation substances (worm castings, fungal chaff, microbial inoculum, and biochar) on the physiological characteristics of maize and the residues of TC and TRGs in the soil-maize system under TC stress. The results showed that TC significantly inhibited growth, disrupted the antioxidant defense system balance, and increased proline and malondialdehyde contents of maize plants. Tetracycline residue contents were significantly higher in root than in shoot, and followed the order root > stem-leaf > grain, which was consistent with the distribution of bioconcentration factors in the different organs of maize plants. The TC residue content in the soil under different treatments was 0.013–1.341 mg kg⁻¹. The relative abundances of different antibiotic resistance genes in the soil-maize system varied greatly, and in maize plants followed the order intI1 > tetW > tetG > tetB > tetM > tetX > tetO. In the soil, tetX had the highest relative abundance, followed by tetG and tetW. A redundancy analysis (RDA) showed that TC was positively correlated with TRGs. The addition of different remediation substances alleviated the toxicity of TC on maize physiological characteristics and reduced the TC and TRG residues in the soil-maize system, with biochar being the best remediation substance. These results provide new insights into the effect of biochar on the migration of TC and TRGs from soil to plants.
... The three studies reported a reduction from 0-log to 1-log after the chlorine-based disinfectant, and this reduction was enhanced significantly after UV-C intervention (5-log to 6-log). This synergistic effect of UV/chlorine has also been demonstrated in drinking water and wastewater disinfection [42,43]. Zeber et al. [30] also assessed UV-C intervention after manual cleaning with other disinfectants such as QAC, obtaining a 6-log reduction after UV-C intervention; even though when manual cleaning was performed with hydrogen peroxide with peracetic acid and with a detergent followed by UV-C disinfection, only 2-log and 1-log reduction, respectively were reached. ...
Article
Full-text available
Aims : During the COVID-19 pandemic the search for complementary methods to enhance manual disinfection in dental and medical practices raised relevance. We sought evidence for the addition of ultraviolet-C (UV-C) disinfection to manual cleaning protocols —and whether it improves the logarithmic (log) reduction of surface pathogen colonies. Methods : This review was registered at the International Prospective Register of Systematic Reviews (PROSPERO) under the number CRD420200193961. Six electronic sources were consulted looking for clinical trials performed in healthcare environments in which pathogens were quantified by colony-forming unit (CFU)-enumeration before and after interventions, all databases were last consulted on May 2021. We assessed the risk of bias using an adapted Revised Cochrane Risk of Bias Tool (RoB 2). The certainty of the evidence was qualified according to the Classification of Recommendations, Evaluation, Development, and Evaluation (GRADE) approach. Results : We identified 1012 records and 12 studies fulfilled the inclusion criteria. All included studies reported enhanced disinfection in the UV-C arm; most of them reported 1-log to 2-log reduction in approximately 10 to 25 minutes. Only three studies reached a 5-log and 6-log reduction. When manual cleaning was performed alone, only two studies reported a 1-log reduction using a chlorine-based disinfectant. We detected a high risk of bias in 1 study. Certainty of evidence was classified as moderate and low. Conclusions : The evidence points out the effectiveness of UV-C technology in reducing manual cleaning failures, enhancing the logarithmic reduction of surface pathogen colonies. However, the safety and success of these devices will depend on several physical and biological factors. A judicious project must precede their use in clinical and medical offices under the supervision of a physicist or other trained professional.
... Live bacteria and ARG-containing DNA are of great importance in the development of antimicrobial resistance in wastewater environments. Conventional wastewater disinfection treatments could effectively deactivate ARB, mitigating the dissemination of ARGs via conjugative gene transfer (Lin et al., 2016). However, ARG-containing DNA released from the cell debris is still conferring resistance genotypes to competent recipient cells via natural transformation and/or transduction (Dodd, 2012), which is ignored in the existing disinfection technologies (e.g., chlorination, UV irradiation, and ozonation). ...
Article
The overuse and misuse of antibiotics in animal breeding for disease treatment and growth enhancement have been major drivers of the occurrence, diffusion, and accumulation of antibiotic resistance genes (ARGs) in wastewater. Strategies to combat ARG dissemination are pressingly needed for human and ecological safety. To achieve this goal, a biochar-based polymer, magnetic biochar/quaternary phosphonium salt (MBQ), was applied in livestock wastewater and displayed a high performance in bacterial deactivation and ARG decrease. Efficient antibacterial effects were achieved by both MBQ and quaternary phosphonium salt; however, the abundance and fold change of ARGs in the MBQ treatment indicated a more powerful ARG dissemination control than quaternary phosphonium salt. The application of MBQ evidently reduced the microbial diversity and may primarily be responsible for altering the ARG profiles in wastewater. Network, redundancy, and variation partitioning analyses were further employed to reveal that the microbial community and the presence of mobile genetic elements were two critical factors shaping the pattern of the antibiotic resistome in livestock wastewater. Considered together, these findings extend the application field of biochar and have important implications for reducing ARG dissemination risks in livestock wastewater.
... From the above results, it was observed that the frequency of [20,53], although this might be because the UV intensity employed in these studies is stronger, reducing the vitality of bacteria in a short time. With exposure to the interface of PC NS+UV365nm and PC NS+SS , inconsistent results were observed, where only a weak increase of the conjugative transfer frequency occurred. ...
Article
Antibiotic-resistance genes (ARGs) dissemination in water environment has raised concerns worldwide. Here, antibiotic-resistant bacteria (ARB) were exposed to the interface of natural sphalerite (NS) irradiated by different light sources (UV254nm, UV365nm, simulated sunlight (SS), and visible light (VL)) in water and their effects on ARG conjugative transfer were studied. The conjugative transfer frequency increased 2- to 10-fold under exposure to Photocatalysis (PC)NS+UV254nm or PCNS+VL and 1- to 2-fold under PCNS+UV365nm or PCNS+SS. During exposure, bacteria were directly stimulated by light irradiation or spontaneous photocatalytic inactivation, triggering oxidative stress, DNA repair, cell repair and transfer regulation of ARB. These results indicated that ARG transfer could be promoted once ARB involving in this environmental PC interface. This new viewpoint revealed that natural minerals with natural light irradiation play an important role in ARG dissemination. Besides, this study provided more detailed information for practical application of PC sterilization and control of ARG transfer.
Article
Antibiotic resistance genes (ARGs) are emerging contaminants, which have been frequently detected in different aquatic environments, posing potential risk to public health and ecosystem. A properly designed and operated wastewater treatment process can be an effective final barrier for reducing the quantity of ARGs discharged into the environment. In order to control the propagation of antimicrobial resistance in the environment, it is essential to comprehensively understand the elimination and inactivation of ARGs by various wastewater treatment processes. This review systematically summarized and analyzed the feasibility and efficiency of ARGs removal in different wastewater treatment processes, including biological processes, such as membrane bioreactor process and constructed wetlands; chemical processes, such as ozonation, chlorination, Fenton oxidation and other advanced oxidation processes (AOPs); physicochemical processes, such as UV radiation, ionizing radiation; and physical processes, such as coagulation and membrane filtration. In addition, the advantages and limitations as well as future direction of these treatment processes for the elimination and inactivation of ARGs in wastewater were also discussed, aiming to provide better understanding and support for future research.
Article
The occurrence of viable but non-culturable (VBNC) bacteria in the wastewater system poses a huge threat to environmental and public health, in particular in hospital wastewater treatment system (HWTS). HWTS-oriented studies have been conducted to assess the effectiveness of chlorination and UV disinfection using indigenous bacteria. Results revealed that the VBNC Escherichia coli and ARGs remained persistent even at high chlorination (12 mg/L for 2.5 h) and UV doses (1000 mJ/cm²). The molecular mechanisms underlying chlorination-/UV-induced VBNC state in E. coli were explored through the transcriptomics and results suggested that most energy-dependent physiological activities (e.g., metabolism) have been suppressed in VBNC E. coli, while the pathogenicity-related genes varied insignificantly compared to the culturable cells, indicating that the VBNC E. coli could potentially display pathogenicity. Further Galleria mellonella model experiment has confirmed that although the disinfection-induced VBNC state made cells less infectious, these cells could regain their pathogenicity after resuscitation. This in vitro study can be used as a reference for studies on infections from VBNC bacteria and highlights the health risk due to VBNC pathogens in hospital effluents. There is a need to develop effluent standards specifically for healthcare facilities, and a stricter downstream disinfection strategy should be considered for the removal of VBNC cells and ARGs in the effluent.
Article
Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are the emerging contaminants leading to a serious worldwide health problem. Although disinfection like ultraviolet (UV) irradiation could remove part of ARB and ARGs, there still are residual ARB and ARGs in the effluent of wastewater treatment plants. Conjugative transfer is main concern of the risk of ARGs and little is known about the effects of UV disinfection on the transfer ability of the non-inactivated ARB in the effluent which will enter the environment. Hence the influences of UV irradiation and reactivation on ARB conjugative transfer ability were studied under laboratory condition, focusing on the survival bacteria from UV irradiation and the reactivated bacteria, as well as their descendants. The experimental results imply that even 1 mJ/cm² UV disinfection can significantly decrease the conjugative transfer frequency of the survival bacteria. However, viable but not culturable state cells induced by UV can reactivate through both photoreactivation and dark repair and retain the same level of transfer ability as the untreated strains. This finding is essential for re-considering about the post safety of UV irradiated effluent and microbial safety control strategies were required.
Article
Antibiotic resistance is extensively detected in drinking water sources, threatening its safety and human health, which deserves further attention to the removal of antibiotic resistance genes (ARGs) in the drinking water system. In this study, the occurrence and reduction of integrase gene intI1 and forty-one ARG subtypes, which confers resistance to six antibiotic classes (β-lactam, aminoglycoside, macrolide, tetracycline, sulfonamide, and quinolone), were investigated in a drinking water treatment plant (DWTP). Seventeen ARG subtypes with absolute concentrations ranging from 1.4 × 10 ⁰ to 7.3 × 10 ⁵ and 3.9 × 10 ⁴ genes/mL (intI1) were detected in the raw water; and sul1 and sul2 were the two dominant ARG subtypes. Overall, the whole DWTPs achieved 0.03–2.4 log reduction of ARGs compared with those presented in raw water. The reduction efficiencies of sul1, strA, and intI1 were the highest (1.0–2.4 log) in both conventional and advanced processes. However, the levels of sul1, sul2, and ermC still remained high (1.3 × 10 ⁰ –1.9 × 10 ⁴ genes/mL) in finished water. The treatment units, including pre-flocculation/sedimentation/sand filtration, and ozonation units, were beneficial for the reduction of ARGs, which was mostly ascribed to the decline in biomass and the strong oxidizing properties of ozone. However, the reduction effect was subsequently counteracted by the granular activated carbon and chlorination units. This study provides basic data for ARG pollution in the drinking water system, and suggests that ARGs persist in drinking water, even after conventional chlorination or advanced treatment processes, highlighting the need for new and efficient water purification technologies.
Article
The long-term persistence of antibiotic resistance in the environment, especially in drinking water, is a public health concern. Expression of an efflux pump, an important mechanism of resistance to antibiotics, usually confers a fitness cost in bacteria. In this study, we aimed to determine why antibiotic resistance conferred by overexpression of an efflux pump persisted in low-nutrient environments (TOC < 10 mg/L) such as drinking and source water in which antibiotic selective pressure might be very low or even absent. Competition experiments between wild-type Pseudomonas aeruginosa and ciprofloxacin-resistant mutants revealed that the fitness cost of ciprofloxacin resistance significantly decreased (p < 0.05) under low-nutrient (0.5 mg/L total organic carbon (TOC)) relative to high-nutrient (500 mg/L TOC) conditions. Mechanisms underlying this fitness cost were analyzed. The mexD gene expression in resistant bacteria (cip_3 strain) was significantly lower (p < 0.05) in low-nutrient conditions, with 10 mg/L TOC ((8.01 ± 0.82)-fold), than in high-nutrient conditions, with 500 mg/L TOC ((48.89 ± 4.16)-fold). Moreover, rpoS gene expression in resistant bacteria ((1.36 ± 0.13)-fold) was significantly lower (p < 0.05) than that in the wild-type strain ((2.78 ± 0.29)-fold) under low-nutrient conditions (10 mg/L TOC), suggesting a growth advantage. Furthermore, the difference in metabolic activity between the two competing strains was significantly smaller (p < 0.05) in low-nutrient conditions (5 and 0.5 mg/L TOC). These results suggest that nutrient levels are a key factor in determining the persistence of antibiotic resistance conferred by efflux pumps in the natural environment with trace amounts or no antibiotics.
Article
Recently, the dissemination of antibiotic resistance genes (ARGs) via plasmid-mediated conjugation has been reported to be facilitated by a series of contaminants. This has highlighted potential challenges to the effective control of this principal mode of horizontal transfer. In the present study, we found that low levels (<0.02 mgN/L) of free nitrous acid (FNA) remarkably inhibited (over 90%) the conjugative transfer of plasmid RP4, a model broad-host-range plasmid, between Escherichia coli. The antimicrobial role of FNA at the applied dosages was firstly ruled out, since no dramatic reductions in viabilities of donor or recipient were observed. Instead, FNA appeared to reduce the available intracellular free Mg2+, which was confirmed to be triggered by the liberation of intracellular Fe2+. These alterations in intracellular Mg2+ and Fe2+ concentrations were found to significantly limit the available energy for conjugative transfer through suppression of glycolysis by decreasing the activities of glycogen phosphorylase and glyceraldehyde-3-phosphate dehydrogenase and also by diverting the glycolytic flux into the pentose phosphate pathway via activation of glucose-6-phosphate dehydrogenase towards the generation of NADPH rather than ATP. Moreover, RP4-encoding genes responsible for DNA transfer and replication (traI, traJ and trfAp), coupling (traG) and mating pair formation (traF and trbBp) were all significantly down-regulated after FNA treatment, indicating that the transfer apparatus required for plasmid processing and delivery was deactivated. By validating the inhibitory effects of FNA on conjugation in real wastewater, this study highlights a promising method for controlling the dissemination of ARGs in systems such as wastewater treatment plants.
Article
In recent years, photocatalysis has been considered as a promising method, which provides measures to environmental pollution. Antibiotic resistant bacteria (ARB) and their antibiotic resistance genes (ARGs), as the emerging environmental pollutants, are released into the environment, resulting in antibiotic resistance spread. TiO2-based nanocomposites, as the most common photocatalytic material, may influence ARB and ARGs under photocatalytic conditions. However, the research on this aspect is rare. A novel nanocomposite synthesized from Ag, TiO2 and graphene oxide (GO), was selected as a representative of nanomaterials for investigation. The experimental results indicated that TiO2/Ag/GO nanocomposites significantly affected ARB vitality. 100 mg/L TiO2/Ag/GO will reduce bacterial survival to 12.2% in 10 min under simulated sunlight irradiation. Chloramphenicol as the most representative antibiotic in the water, reduces the effect of ARB inactivation under photocatalytic conditions. The addition of TiO2/Ag/GO could affect tetracycline antibiotic resistance. The level of bacterial tolerance to tetracycline had a significant reduction. The horizontal gene transfer was promoted from 1 to 2 folds with the addition of TiO2/Ag/GO. Even high TiO2/Ag/GO concentration (100 mg/L) sample had a limited promotion, suggesting that TiO2/Ag/GO will not increase the risk of antibiotic resistance spread compared to other nano materials.
Article
Antibiotic resistance has created obstacles in the treatment of infectious diseases with antibiotics. The horizontal transfer of antibiotic resistance genes (ARGs) can exacerbate the dissemination of antibiotic resistance in water environments. In addition to antibiotic selective pressure, multiple non-antibiotic factors can affect the horizontal transfer of ARGs. Herein, we seek to comprehensively review the effects and relevant mechanisms of non-antibiotic factors on the horizontal transfer of ARGs in water environments, especially contaminants from human activities and water treatment processes. Four pathways have been identified to accomplish horizontal gene transfer (HGT), i.e., conjugation, transformation, transduction, and vesiduction. Changes in conjugative frequencies by non-antibiotic factors are mainly related to their concentrations, which conform to hormesis. Relevant mechanisms involve the alteration in cell membrane permeability, reactive oxygen species, SOS response, pilus, and mRNA expression of relevant genes. Transformation induced by extracellular DNA may be more vulnerable to non-antibiotic factors than other pathways. Except bacteriophage infection, the effects of non-antibiotic factors on transduction exhibit many similarities with that of conjugation. Given the secretion of membrane vesicles stimulated by non-antibiotic factors, their effects on vesiduction can be inferred. Furthermore, contaminants from human activities at sub-inhibitory or environmentally relevant concentrations usually promote HGT, resulting in further dissemination of antibiotic resistance. The horizontal transfer of ARGs is difficult to be inhibited by individual water treatment processes (e.g., chlorination, UV treatment, and photocatalysis) unless they attain sufficient intensity. Accordingly, the synergistic application containing two or more water treatment processes is recommended. Overall, we believe this review can elucidate the significance for risk assessments of contaminants from human activities and provide insights into the development of environment-friendly and cost-efficient water treatment processes to inhibit the horizontal transfer of ARGs.
Article
Antibiotic resistant bacteria (ARB) and resistance genes (ARGs) are emerging environmental pollutants with strong pathogenicity. In this study, surface plasma was developed to inactivate the donor ARB with Escherichia coli (AR E. coli) as a model, eliminate ARGs, and inhibit conjugative transfer of ARGs in water, highlighting the influences of concomitant inorganic ions. Surface plasma oxidation significantly inactivated AR E. coli, eliminated ARGs, and inhibited conjugative transfer of ARGs, and the presence of NO3⁻, Cu²⁺, and Fe²⁺ all promoted these processes, and SO4²⁻ did not have distinct effect. Approximately 4.5log AR E. coli was inactivated within 10 min treatment, and it increased to 7.4log AR E. coli after adding Fe²⁺. Integrons intI1 decreased by 3.10log (without Fe²⁺) and 4.43log (adding Fe²⁺); the addition of Fe²⁺ in the surface plasma induced 99.8% decline in the conjugative transfer frequency. The inhibition effects on the conjugative transfer of ARGs were mainly attributed to the reduced reactive oxygen species levels, decreased DNA damage-induced response, decreased intercellular contact, and down-regulated expression of plasmid transfer genes. This study disclosed underlying mechanisms for inhibiting ARGs transfer, and supplied a prospective technique for ARGs control.
Article
Antibiotic resistance genes (ARGs) pose a serious threat to public health. Wastewater treatment plants (WWTPs) are essential for controlling the release of ARGs into the environment. This study investigated ARG distribution at every step in the treatment process of a municipal WWTP located in Harbin for six consecutive months. Changes in ARG distribution involved in two advanced secondary effluent treatment processes, ozonation and granular activated carbon (GAC) adsorption, were analyzed. Biological treatment resulted in the highest ARG removal (0.76–1.94 log reduction), followed by ultraviolet (UV) disinfection (less than 0.5-log reduction). Primary treatment could not significantly remove ARGs. ARG removal efficiency increased with an increase in the ozone dose below 40 mg/L. However, amorphous GAC (AGAC) adsorption with a hydraulic retention time (HRT) of 1 h showed better removal of ARGs, total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) than ozonation at a 60 mg/L dose. UV treatment could efficiently reduce the relative ARG abundance, despite presenting the lowest efficiency for the reduction of absolute ARG abundance compared with GAC and ozone treatments. The combination of ozone and AGAC can significantly improve the removal of ARGs, TOC, TN and TP. These results indicate that a treatment including biological processing, ozonation, and AGAC adsorption is a promising strategy for removing ARGs and refractory organic substances from sewage.
Article
Phenolic compounds are common organic pollutants in wastewater. During the wastewater treatment process, these compounds may influence the microbial community structure and functions. However, the impact of the phenolic compounds in the wastewater treatment plants (WWTP) on the horizontal transfer of antibiotic resistance genes (ARGs) has not been well assessed. In this study, we investigated the horizontal transfer of ARGs under the stress of phenolic compounds. The results showed that in pure culture bacteria system, p-nitrophenol (PNP), p-aminophenol (PAP) and phenol (PhOH) (10–100 mg/L) can significantly increase the horizontal transfer frequency of ARGs by 2.2–4.6, 3.6–9.4 and 1.9–9.0 fold, respectively. And, the RP4 plasmid transfer from Escherichia coli HB101 (E. coli HB101) to the bacteria in activated sludge increased obviously under the stress of phenolic compounds. Further investigation revealed that the PNP and PhOH at the concentration of 10–100 mg/L increased the production of reactive oxygen species (ROS) and the permeability of cell membrane in the donor and recipient, which could be the causes of horizontal transfer of RP4 plasmid. In addition, it was also found that PNP, PAP and PhOH stress inhibit the expression of the global regulatory genes korB and trbA in the RP4 plasmid, and increase the expression level of the traF gene, thereby promoting the conjugative transfer of the RP4 plasmid. Taken together, these results improved our understanding of the horizontal transfer of ARGs under the stress of phenolic compounds and provided basic information for management of the systems that treat wastewater containing phenolic compounds.
Article
For comprehensive insights into the effects of disinfection strategy on antibiotic resistance genes (ARGs) in pipe wall biofilm to ensure the biosafety of domestic hot water system (DHWS), this study investigated the occurrence, removal and interactions of ARGs, as well as their potential hosts. The shifts in biofilm community composition and microbial functions (level three) were observed under different disinfection strategies. A total of 40 ARG subtypes within seven antibiotic types were predicted. The total gene counts ranged from 6.10 × 10⁴ to 2.31 × 10⁵, and decreased after the chlorine, chlorine dioxide, silver ions (Ag⁺), ultraviolet (UV), and Ag⁺-UV disinfection. The ARGs in samples under different disinfection strategies were divided into four groups, and the removal and enrichment of the same ARGs in each group were almost consistent. The complex interactions among ARGs were weakened and altered by disinfection (edges decreased from 237 to 178), with yebQ and marC as the hub ARGs, but positive correlations were still dominant. Moreover, 36 nonpathogenic bacteria, including high- (Blastocatella), mid- (Ornatilinea) and low-abundant genera (Bdellovibrio), as well as 18 potential pathogens (Vibrio and Bacillus) were identified as the potential hosts harboring ARGs. Overall, this study provides some new insights into the occurrence of ARGs and their fate under eight disinfection strategies, which is of great significance for a comprehensive understanding and control of ARGs in DHWS.
Chapter
The intensive use of antibiotics for medical, veterinary, or agricultural purposes results in the continuous release of antibiotics into the environment, leading to the increasingly widespread occurrence of antibiotic resistance. Although antibiotic resistance has been recognized as a major threat to human health worldwide, the related phenomenon occurring in natural and engineered environments has so far been largely overlooked. The urban (including industrial) water cycle, which connects urban life, agriculture, and the environment, is potentially a hot spot for the spread of antibiotic resistance. Therefore, better understanding of the distribution and transportation of antibiotic-resistant bacteria (ARB) and acquisition of antibiotic resistance genes (ARGs) in the urban water cycle is critically important to improve the control of this emerging environmental and human health challenge. In this book chapter, we comprehensively review the occurrence, transfer, and acquisition mechanisms of ARGs in the urban water cycle. Various methods that are used to monitor ARB and ARGs are compared in terms of their strengths and limitations. Opportunities for the development of real-time monitoring methods are discussed, along with possible control strategies for ARB and ARGs in urban water environments. We recommend that three major barriers should be developed to minimize or halt the spread of ARGs in urban water systems, including more efficient water disinfection, advanced wastewater treatment, and optimized sludge treatment processes.
Article
The integration of bioelectrochemical system (BES) into conventional anaerobic composting process can accelerate the degradation of excess dewatered sludge (ES). However, no reports have been made concerning antibiotic resistance genes (ARGs) profile and abundance in BESs fuelled with ES, and the effect of CaO2 on the fate of ARGs within BESs treating excess sludge has rarely been investigated. The aim of this study was to investigate the effect of CaO2 and the bioelectrochemical process on the abundances of ARGs and MGEs and to unravel the mechanism of ARGs attenuation. Results showed that CaO2 addition could enhance the reduction of ARG levels in ES within AnCBE. The mean ARG abundances in the AnCBE samples with high CaO2 doses (0.4 g CaO2/g VSS and 0.5 g CaO2/g VSS) were significantly lower than the values in samples with other CaO2 doses. The abundances of lincosamide nucleotidyltransferase, macB, macrolide transporter ATP-binding proteins, and macrolide-efflux proteins significantly decreased with the increase in the CaO2 dose. Both CaO2 addition and bioelectrochemical assistance played important roles in shaping the ARG composition during the AnCBE process. The variation in the microbial community composition is the most important contributor to the variation in the ARGs composition. The abundances of Actinobacteria and Firmicutes explained 52.8% of the total ARG variance. Of the MGEs, the abundances of plasmids, insertion sequences, and integrons were all reduced in the sludge metagenomes. There was a significantly positive correlation between the abundances of sulI, sulII, tetG, and blaTEM and those of metal resistance genes (MRGs), which decreased significantly after the AnCBE process. This study revealed the potential of the combination of CaO2 and bioelectrogenesis for ARG attenuation.
Article
Antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) were investigated from effluent of two hospital and two municipal wastewater treatment plants (WWTPs) before and after disinfection. The results of network analysis showed that 8 genera were identified to be the main potential hosts of ARGs, including Mycobacterium, Ferruginibacter, Thermomonas, Morganella, Enterococcus, Bacteroides, Myroides and Romboutsia. The removal of ARGs and their possible bacterial hosts were synchronous and consistent by chlorine or ultraviolet (UV) disinfection in WWTPs. The mechanisms of ARB and ARGs removal, and conjugation transfer of RP4 plasmids by UV, chlorine and synergistic UV/chlorine disinfection was revealed. Compared to UV alone, ARB inactivation was improved 1.4 log and photoreactivation was overcome effectively by UV/chlorine combination (8 mJ/cm², chlorine 2 mg/L). However, ARGs degradation was more difficult than ARB inactivation. Until UV dosage enhanced to 320 mJ/cm², ARGs achieved 0.58-1.60 log removal. Meanwhile, when 2 mg/L of chlorine was combined with UV combination, ARGs removal enhanced 1-1.5 log. The synergistic effect of adding low-dose chlorine (1-2 mg/L) during UV radiation effectively improved ARB and ARGs removal simultaneously. The same synergistic effect also occurred in the horizontal gene transfer (HGT). Non-lethal dose chlorine (0.5 mg/L) increased the conjugation transfer frequency, which confirmed that the mRNA expression levels of type IV secretion system (T4SS) proteins vir4D, vir5B and vir10B were significantly enhanced. The risk of RP4 plasmid conjugation transfer was significantly reduced with UV/chlorine (UV ≥ 4 mJ/cm², chlorine ≥ 1 mg/L). These findings may serve as valuable implications for assessing and controlling the risk of ARGs transfer and propagation in the environment.
Article
Disinfection technologies, especially light-based disinfection, have undergone tremendous development and innovation, but this treatment can cause bacteria to enter viable but nonculturable (VBNC) state. Due to their strong tolerance, VBNC bacteria cannot be completely removed by disinfection technologies, thereby posing a potential risk for antibiotic resistance gene (ARG) transfer. Therefore, to better understand VBNC bacteria and interpret potential transfer of ARGs, this article systematically reviewed changes in morphology, physiology and virulence of bacteria after entering VBNC state. In addition, this article reviewed quantitative detection methods of VBNC bacteria, such as cell membrane integrity-mediated LIVE/DEAD Baclight assay, qPCR-based assays, and phage-based detection methods, concluding that there is still a lack of in-situ and real-time detection methods for VBNC bacteria. Health risks and environmental application value of VBNC bacteria were then valuated, with data indicating that VBNC bacteria have great value in the domain of microbial utilization. Furthermore, the induction conditions (especially by light-based disinfection) and formation mechanisms of VBNC bacteria were highlighted. Formation mechanisms mainly involve stringent response, general stress response system and toxin-antitoxin (TA) system. Moreover, horizontal gene transfer (HGT) of ARGs during and after the formation of VBNC bacteria induced by light-based disinfection was evaluated. It was found that ARGs may be transferred through conjugation, transformation and transduction. Finally, current deficiencies and future challenges for the transformation of VBNC bacteria, especially those influenced by light-based disinfection technologies, were summarized. This review provides new insights into detection methods, formation mechanisms, environmental applications and potential ARG transfer risks of VBNC bacteria.
Article
Globally, the challenges with extensive consumption and improper disposal of antibiotics have become a menace to public health. This anomaly has contributed to the emergence and spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the environment. Many of these resistance genes are carried on plasmids, transposons, or integrons, and their origin is linked to anthropogenic sources. Wastewater treatment plants (WWTPs) harbors a vast diversity of microorganisms and are responsible for disseminating ARB/ARGs. The failure of different treatment methods/materials to address the challenges observed with antibiotics resistance in wastewater treatment facilities alters access to quality water in the ecosystem. This paper emphasized the health implication of antibiotic resistance in wastewater and its effect and the pathways for their dissemination from wastewater into receiving waters. Furthermore, the lack of quality data and efforts in removing antibiotics-resistant bacteria and their genes were mentioned in this paper compared to the abundance of data on the prevalence or incidences of these substances in wastewater. Potentials of metallic nanoparticles and their unique properties as a treatment option for removing DNA conveying ARGs from wastewater treatment plants were critically discussed in this paper. Also, other treatment options and their limitations have been extensively discussed. Lastly, this review also highlights the importance of regulating antibiotics and their indiscriminate use.
Article
Antibiotic resistance has gained increasing attention worldwide, and wastewater treatment plants have been regarded as hotspots for antibiotic-resistant bacteria and antibiotic-resistant genes (ARGs). In this study, we evaluated the removal of tetracycline-resistant Escherichia coli and its related genes through ultrasound (US) treatment with different input levels of US-specific energy combined with ultraviolet light emitting diodes (UV-LEDs). Simultaneous US with UV-LEDs effectively eliminated tetracycline-resistant E. coli with the normal suggested UV-LEDs dosage (below 30 mJ/cm²). The removal efficiency increased with the addition of US (specific input energy of 8–16 kJ/L), and simultaneous US treatment with UV-LEDs was relatively more effective than US pretreatment. Analyses of cell damage by K⁺ leakage and flow cytometry showed that the cell wall kept its integrity during the applied treatment conditions. Consequently, the removal efficiencies of 16S rRNA, tet M, and tet Q were unsatisfactory because less than 1 log reduction was achieved. Increasing the US energy remarkably damaged the cell wall and potentially promoted the reaction. The removal of ARGs increased four times when using US-specific input energy at 330 kJ/L with 5 mJ/cm² compared with UV-LEDs alone. The US treatment combined with UV-LEDs is a novel process that does not require chemicals. Results of this research can provide theoretical support for the removal of ARGs.
Article
Bacterial antibiotic resistance in water environments is becoming increasingly severe, and new antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) have also attracted the attention of researchers. The horizontal transfer of ARGs in water environments is considered one of the main sources of bacterial resistance in the natural environment. Horizontal gene transfer (HGT) mainly includes conjugation, natural transformation, and transduction, and conjugation has been investigated most. Several studies have shown that there are a large number of environmental factors that might affect the horizontal transfer of ARGs in water environments, such as nanomaterials, various oxidants, and light; however, there is still a lack of systematic and comprehensive reviews on the detection and the effects of the influence factors of on ARG horizontal transfer. Therefore, this study introduced three HGT modes, analysed the advantages and disadvantages of current methods for monitoring HGT, and then summarized the influence and mechanism of various factors on ARG horizontal transfer, and the possible reasons for the different effects caused by similar factors were mainly critically discussed. Finally, existing research deficiencies and future research directions of ARG horizontal transfer in water environments were discussed.
Article
Both microplastic and bacterial antibiotic resistance have attracted attention worldwide. When microplastics coexist with antibiotic-resistant bacteria (ARB), which carry antibiotic resistance genes (ARGs), ARB colonize the surface of microplastics, and a unique biofilm is formed. The ARB and ARGs in biofilms are denser and more difficult to remove. However, studies on the factors influencing the formation of microplastic biofilms are limited. In this study, plasmid RP4, which appeared in wastewater treatment plants, was found to be able to promote irreversible bacterial colonization of microplastics, and the hypothetical reason was conjugative pili expression. Then, the potential conjugative pili synthesis promoter “nanoalumina” and inhibitor “free nitrous acid” (FNA) were selected to test this hypothesis. Simultaneously, nanoalumina promoted and FNA inhibited bacterial colonization when RP4 existed. Combined with the gene expression and ATP analysis results, this hypothesis was confirmed, and the mechanism of RP4 on bacterial colonization was related mainly to conjugative pili protein synthesis and intracellular ATP. In this study, the effects of plasmid RP4, nanoalumina, and FNA on the formation of microplastic biofilms were reported, which has a certain reference value for other researchers exploring microplastic biofilms.
Article
Full-text available
The purpose of a drinking water distribution system is to deliver drinking water to the consumer, preferably with the same quality as when it left the treatment plant. In this context, the maintenance of good microbiological quality is often referred to as biological stability, and the addition of sufficient chlorine residuals is regarded as one way to achieve this. The full-scale drinking water distribution system of Riga (Latvia) was investigated with respect to biological stability in chlorinated drinking water. Flow cytometric (FCM) intact cell concentrations, intracellular adenosine tri-phosphate (ATP), heterotrophic plate counts and residual chlorine measurements were performed to evaluate the drinking water quality and stability at 49 sampling points throughout the distribution network. Cell viability methods were compared and the importance of extracellular ATP measurements was examined as well. FCM intact cell concentrations varied from 5×103 cells mL-1 to 4.66×105 cells mL-1 in the network. While this parameter did not exceed 2.1×104 cells mL-1 in the effluent from any water treatment plant, 50% of all the network samples contained more than 1.06×105 cells mL-1. This indisputably demonstrates biological instability in this particular drinking water distribution system, which was ascribed to a loss of disinfectant residuals and concomitant bacterial growth. The study highlights the potential of using cultivation-independent methods for the assessment of chlorinated water samples. In addition, it underlines the complexity of full-scale drinking water distribution systems, and the resulting challenges to establish the causes of biological instability.
Article
Full-text available
The outer membrane porin proteins are the major factors in controlling the permeability of cell membrane. OmpF is an example of porin proteins in Esherichia coli. In normal growth condition a large amount of this protein is synthesised, but under stress condition, such as the presence of antibiotics in environment its expression is decreased inhibiting the entrance of antibiotics into cell. The expression of ompF is inhibited by antisense RNA transcribed from micF. In normal condition the expression of micF is low, but in the presence of antibiotics its expression is increased and causes multiple resistances to irrelevant antibiotics. The aims of this research were to study first, the intactness of micF and then quantify the expression of ompF in ciprofloxacin and tetracycline resistant mutants of E. coli. For this purpose the 5' end of micF was amplified and then sequenced. None of these mutants except one and its clone has a mutation in this gene. Then the relative expression of ompF in these mutants was quantified by real time PCR. There was no significant difference between ompF transcription of mutants and wild type strain. Based on this study and previous study it is concluded that low to intermediate levels of resistance to ciprofloxacin and tetracycline does not decrease ompF transcription.
Article
Full-text available
Antibiotics are among the most successful group of pharmaceuticals used for human and veterinary therapy. However, large amounts of antibiotics are released into municipal wastewater due to incomplete metabolism in humans or due to disposal of unused antibiotics, which finally find their ways into different natural environmental compartments. The emergence and rapid spread of antibiotic resistant bacteria (ARB) has led to an increasing concern about the potential environmental and public health risks. ARB and antibiotic resistant genes (ARGs) have been detected extensively in wastewater samples. Available data show significantly higher proportion of antibiotic resistant bacteria contained in raw and treated wastewater relative to surface water. According to these studies, the conditions in wastewater treatment plants (WWTPs) are favourable for the proliferation of ARB. Moreover, another concern with regards to the presence of ARB and ARGs is their effective removal from sewage. This review gives an overview of the available data on the occurrence of ARB and ARGs and their fate in WWTPs, on the biological methods dealing with the detection of bacterial populations and their resistance genes, and highlights areas in need for further research studies.
Article
Full-text available
Antibiotic resistance genes (ARGs) are emerging contaminants posing a potential worldwide human health risk. Intensive animal husbandry is believed to be a major contributor to the increased environmental burden of ARGs. Despite the volume of antibiotics used in China, little information is available regarding the corresponding ARGs associated with animal farms. We assessed type and concentrations of ARGs at three stages of manure processing to land disposal at three large-scale (10,000 animals per year) commercial swine farms in China. In-feed or therapeutic antibiotics used on these farms include all major classes of antibiotics except vancomycins. High-capacity quantitative PCR arrays detected 149 unique resistance genes among all of the farm samples, the top 63 ARGs being enriched 192-fold (median) up to 28,000-fold (maximum) compared with their respective antibiotic-free manure or soil controls. Antibiotics and heavy metals used as feed supplements were elevated in the manures, suggesting the potential for coselection of resistance traits. The potential for horizontal transfer of ARGs because of transposon-specific ARGs is implicated by the enrichment of transposases-the top six alleles being enriched 189-fold (median) up to 90,000-fold in manure-as well as the high correlation (r(2) = 0.96) between ARG and transposase abundance. In addition, abundance of ARGs correlated directly with antibiotic and metal concentrations, indicating their importance in selection of resistance genes. Diverse, abundant, and potentially mobile ARGs in farm samples suggest that unmonitored use of antibiotics and metals is causing the emergence and release of ARGs to the environment.
Chapter
Full-text available
“Biofouling” is referred to as the unwanted deposition and growth of biofilms. This phenomenon can occur in an extremely wide range of opportunities ranging from colonization of medical devices, during production of ultrapure drinking and process water, and fouling of ship hulls, pipelines and reservoirs. Although biofouling occurs in such different areas, it has a common cause, which is the biofilm. Biofilms are the most successful form of life on earth and tolerate high concentrations of biocidal substances. Conventional anti-fouling approaches usually rely on the efficacy of biocides, aiming for inhibition of biofilm growth. It is important to keep in mind that killing of biofilm organisms usually does not solve biofouling problems as mostly the biomass is the problem and must be removed. Therefore, cleaning is at least equally important. However, for a sustainable anti-fouling strategy, an advanced approach is suggested, which includes the analysis of the fouling situation, a selection of suitable components of the “anti-fouling menu” and an effective and representative monitoring of biofilm development. One important part of this menu is nutrient limitation, which could be implemented on a much broader scale than is practiced today. Other items on the menu include methods to monitor unwanted biofilm development and assessment of the efficacy of anti-fouling measures. Also, natural anti-fouling strategies are worth exploring and learning from — and nature never relies on only one defence line but on integrated approaches.
Article
Full-text available
Recent research has revealed that horizontal gene transfer and biofilm formation are connected processes. Although published research investigating this interconnectedness is still limited, we will review this subject in order to highlight the potential of these observations because of their believed importance in the understanding of the adaptation and subsequent evolution of social traits in bacteria. Here, we discuss current evidence for such interconnectedness centred on plasmids. Horizontal transfer rates are typically higher in biofilm communities compared with those in planktonic states. Biofilms, furthermore, promote plasmid stability and may enhance the host range of mobile genetic elements that are transferred horizontally. Plasmids, on the other hand, are very well suited to promote the evolution of social traits such as biofilm formation. This, essentially, transpires because plasmids are independent replicons that enhance their own success by promoting inter-bacterial interactions. They typically also carry genes that heighten their hosts' direct fitness. Furthermore, current research shows that the so-called mafia traits encoded on mobile genetic elements can enforce bacteria to maintain stable social interactions. It also indicates that horizontal gene transfer ultimately enhances the relatedness of bacteria carrying the mobile genetic elements of the same origin. The perspective of this review extends to an overall interconnectedness between horizontal gene transfer, mobile genetic elements and social evolution of bacteria.
Article
Full-text available
OmpF is one of the major general porins of Enterobacteriaceae that belongs to the first line of bacterial defense and interactions with the biotic as well as abiotic environments. Porins are surface exposed and their structures strongly reflect the history of multiple interactions with the environmental challenges. Unfortunately, little is known on diversity of porin genes of Enterobacteriaceae and the genus Yersinia especially. We analyzed the sequences of the ompF gene from 73 Yersinia strains covering 14 known species. The phylogenetic analysis placed most of the Yersinia strains in the same line assigned by 16S rDNA-gyrB tree. Very high congruence in the tree topologies was observed for Y. enterocolitica, Y. kristensenii, Y. ruckeri, indicating that intragenic recombination in these species had no effect on the ompF gene. A significant level of intra- and interspecies recombination was found for Y. aleksiciae, Y. intermedia and Y. mollaretii. Our analysis shows that the ompF gene of Yersinia has evolved with nonrandom mutational rate under purifying selection. However, several surface loops in the OmpF porin contain positively selected sites, which very likely reflect adaptive diversification Yersinia to their ecological niches. To our knowledge, this is a first investigation of diversity of the porin gene covering the whole genus of the family Enterobacteriaceae. This study demonstrates that recombination and positive selection both contribute to evolution of ompF, but the relative contribution of these evolutionary forces are different among Yersinia species.
Article
Full-text available
Reports state that chlorination of drinking water and wastewater affects the proportions of antibiotic-resistant bacteria by potentially assisting in microbial selection. Studies on the effect of chlorination on like species of antibiotic-resistant bacteria, however, have shown to be conflicting; furthermore, few studies have inspected the regrowth or reactivation of antibiotic-resistant bacteria after chlorination in wastewater. To understand the risks of chlorination resulting from potentially selecting for antibiotic-resistant bacteria, inactivation and reactivation rates of both total heterotrophic bacteria and antibiotic-resistant bacteria (including penicillin-, ampicillin-, tetracycline-, chloramphenicol-, and rifampicin-resistant bacteria) were examined after chlorinating secondary effluent samples from a municipal wastewater treatment plant in this study. Our experimental results indicated similar inactivation rates of both total heterotrophic bacteria and antibiotic-resistant bacteria. Microbial community composition, however, was affected by chlorination: treating samples with 10 mg Cl(2)/L for 10 min resulted in chloramphenicol-resistant bacteria accounting for nearly 100% of the microbial population in contrast to 78% before chlorination. This trend shows that chlorination contributes to selection of some antibiotic-resistant strains. Reactivation of antibiotic-resistant bacteria occurred at 2.0 mg Cl(2)/L for 10 min; specifically, chloramphenicol-, ampicillin-, and penicillin-resistant bacteria were the three prevalent groups present, and the reactivation of chloramphenicol-resistant bacteria exceeded 50%. Regrowth and reactivation of antibiotic-resistant bacteria in secondary effluents after chlorination with a long retention time could threaten public health security during wastewater reuse.
Article
Full-text available
A total of 35 bacteria from contaminated soil (cultivated fields) near pesticide industry from Chinhat, Lucknow, (India) were isolated and tested for their tolerance/resistance to pesticides, heavy metals and antibiotics. Bacterial isolates were identified by 16S rDNA sequencing. Gas Chromatography analysis of the soil samples revealed the presence of lindane at a concentration of 547 ng g(-1) and α-endosulfan and β-endosulfan of 422 ng g(-1) and 421 ng g(-1) respectively. Atomic Absorption Spectrophotometry analysis of the test sample was done and Cr, Zn, Ni, Fe, Cu and Cd were detected at concentrations of 36.2, 42.5, 43.2, 241, 13.3 and 11.20 mg kg(-1) respectively. Minimum inhibitory concentrations of all the isolates were determined for pesticides and heavy metals. All the multi-resistant/tolerant bacterial isolates were also tested for the presence of incompatibility (Inc) group IncP, IncN, IncW, IncQ plasmids and for rolling circle plasmids of the pMV158-family by PCR. Total community DNA was extracted from pesticide contaminated soil. PCR amplification of the bacterial isolates and soil DNA revealed the presence of IncP-specific sequences (trfA2 and oriT) which was confirmed by dot blot hybridization with RP4-derived DIG-labelled probes. Plasmids belonging to IncN, IncW and IncQ group were neither detected in the bacterial isolates nor in total soil DNA. The presence of conjugative or mobilizable IncP plasmids in the isolates indicate that these bacteria have gene transfer capacity with implications for dissemination of heavy metal and antibiotic resistance genes. We propose that IncP plasmids are mainly responsible for the spread of multi-resistant bacteria in the contaminated soils.
Article
Full-text available
Single- and multispecies biofilms formed by six drinking water-isolated bacterial species were used to assess their susceptibilities to sodium hypochlorite (SHC). In general, multispecies biofilms were more resistant to inactivation and removal than single biofilms. Total biofilm inactivation was achieved only for Acinetobacter calcoaceticus single-species biofilms and for those multispecies biofilms without A. calcoaceticus. Biofilms with all bacteria had the highest resistance to SHC, while those without A. calcoaceticus were the most susceptible. A. calcoaceticus formed single biofilms susceptible to SHC; however, its presence in multispecies biofilms increased their resistance to disinfection.
Article
Full-text available
Plasmids are important vehicles for horizontal gene transfer and rapid adaptation in bacteria, including the spread of antibiotic resistance genes. Conjugative transfer of a plasmid from a plasmid-bearing to a plasmid-free bacterial cell requires contact and attachment of the cells followed by plasmid DNA transfer prior to detachment. We introduce a system of differential equations for plasmid transfer in well-mixed populations that accounts for attachment, DNA transfer, and detachment dynamics. These equations offer advantages over classical mass-action models that combine these three processes into a single "bulk" conjugation rate. By decomposing the process of plasmid transfer into its constituent parts, this new model provides a framework that facilitates meaningful comparisons of plasmid transfer rates in surface and liquid environments. The model also allows one to account for experimental and environmental effects such as mixing intensity. To test the adequacy of the model and further explore the effects of mixing on plasmid transfer, we performed batch culture experiments using three different plasmids and a range of different mixing intensities. The results show that plasmid transfer is optimized at low to moderate shaking speeds and that vigorous shaking negatively affects plasmid transfer. Using reasonable assumptions on attachment and detachment rates, the mathematical model predicts the same behavior.
Article
Full-text available
The occurrence and spread of antibiotic-resistant bacteria (ARB) are pressing public health problems worldwide, and aquatic ecosystems are a recognized reservoir for ARB. We used culture-dependent methods and quantitative molecular techniques to detect and quantify ARB and antibiotic resistance genes (ARGs) in source waters, drinking water treatment plants, and tap water from several cities in Michigan and Ohio. We found ARGs and heterotrophic ARB in all finished water and tap water tested, although the amounts were small. The quantities of most ARGs were greater in tap water than in finished water and source water. In general, the levels of bacteria were higher in source water than in tap water, and the levels of ARB were higher in tap water than in finished water, indicating that there was regrowth of bacteria in drinking water distribution systems. Elevated resistance to some antibiotics was observed during water treatment and in tap water. Water treatment might increase the antibiotic resistance of surviving bacteria, and water distribution systems may serve as an important reservoir for the spread of antibiotic resistance to opportunistic pathogens.
Article
Full-text available
The use of antibiotics may accelerate the development of antibiotic resistance genes (ARGs) and bacteria which shade health risks to humans and animals. The emerging of ARGs in the water environment is becoming an increasing worldwide concern. Hundreds of various ARGs encoding resistance to a broad range of antibiotics have been found in microorganisms distributed not only in hospital wastewaters and animal production wastewaters, but also in sewage, wastewater treatment plants, surface water, groundwater, and even in drinking water. This review summarizes recently published information on the types, distributions, and horizontal transfer of ARGs in various aquatic environments, as well as the molecular methods used to detect environmental ARGs, including specific and multiplex PCR (polymerase chain reaction), real-time PCR, DNA sequencing, and hybridization based techniques.
Article
Full-text available
Injury induced in Escherichia coli cells by chlorination was studied from a physiological standpoint. Predictable and reproducible injury was found to occur rapidly in 0.5 mg of chlorine per liter and was reversible under nonselective conditions. There was an extended lag period in the growth of chlorinated cells not seen in control suspensions followed by the resumption of logarithmic growth at a rate equaling that of control cells. The aldolase activity of cells chlorinated in vivo was equivalent to that obtained for control cells. Oxygen uptake experiments showed that chlorinated cells underwent a decrease in respiration that was not immediatedly repaired in the presence of reducing agents. This effect was more pronouned in rich media containing reducing agents. Uptake of metabolities was inhibited by chlorine injury as shown with experiments using 14C-labeled glucose and algal protein hydrolysate.
Article
Full-text available
The broad-host-range vectors pSUP104, pSUP106, pSUP204, pSUP304, and pSUP404 are based on conventional Escherichia coli vectors (such as pBR325 and pACYC184) which have been modified to include the mobilization and broad-host-range replication functions of the IncQ plasmid RSF1010. These vector plasmids now can be maintained in a wide range of bacterial genera including Rhizobium, Agrobacterium, and Pseudomonas. They are efficiently mobilized by RP4 and thus are of particular interest for bacteria refractory to transformation. They offer the selection markers and cloning sites characteristic of the basic E. coli vectors. Therefore, they can be applied and adapted to a variety of cloning strategies. However, the cloning of very large fragments (e.g., in cosmid hybrids of pSUP106) was found to affect the stability of the recombinant molecules in a Rec+ background. This instability was not observed with smaller inserts of about 5 kilobases.
Article
Full-text available
Plasmid conjugation systems are composed of two components, the DNA transfer and replication system, or Dtr, and the mating pair formation system, or Mpf. During conjugal transfer an essential factor, called the coupling protein, is thought to interface the Dtr, in the form of the relaxosome, with the Mpf, in the form of the mating bridge. These proteins, such as TraG from the IncP1 plasmid RP4 (TraG(RP4)) and TraG and VirD4 from the conjugal transfer and T-DNA transfer systems of Ti plasmids, are believed to dictate specificity of the interactions that can occur between different Dtr and Mpf components. The Ti plasmids of Agrobacterium tumefaciens do not mobilize vectors containing the oriT of RP4, but these IncP1 plasmid derivatives lack the trans-acting Dtr functions and TraG(RP4). A. tumefaciens donors transferred a chimeric plasmid that contains the oriT and Dtr genes of RP4 and the Mpf genes of pTiC58, indicating that the Ti plasmid mating bridge can interact with the RP4 relaxosome. However, the Ti plasmid did not mobilize transfer from an IncQ relaxosome. The Ti plasmid did mobilize such plasmids if TraG(RP4) was expressed in the donors. Mutations in traG(RP4) with defined effects on the RP4 transfer system exhibited similar phenotypes for Ti plasmid-mediated mobilization of the IncQ vector. When provided with VirD4, the tra system of pTiC58 mobilized plasmids from the IncQ relaxosome. However, neither TraG(RP4) nor VirD4 restored transfer to a traG mutant of the Ti plasmid. VirD4 also failed to complement a traG(RP4) mutant for transfer from the RP4 relaxosome or for RP4-mediated mobilization from the IncQ relaxosome. TraG(RP4)-mediated mobilization of the IncQ plasmid by pTiC58 did not inhibit Ti plasmid transfer, suggesting that the relaxosomes of the two plasmids do not compete for the same mating bridge. We conclude that TraG(RP4) and VirD4 couples the IncQ but not the Ti plasmid relaxosome to the Ti plasmid mating bridge. However, VirD4 cannot couple the IncP1 or the IncQ relaxosome to the RP4 mating bridge. These results support a model in which the coupling proteins specify the interactions between Dtr and Mpf components of mating systems.
Article
Full-text available
The relationship between cell inactivation and membrane damage was studied in two gram-positive organisms, Listeria monocytogenes and Bacillus subtilis, and two gram-negative organisms, Yersinia enterocolitica and Escherichia coli, exposed to chlorine in the absence and presence of 150 ppm of organic matter (Trypticase soy broth). L. monocytogenes and B. subtilis were more resistant to chlorine in distilled water. The addition of small amounts of organic matter to the chlorination medium drastically increased the resistance of both types of microorganisms, but this effect was more marked in Y. enterocolitica and E. coli. In addition, the survival curves for these microorganisms in the presence of organic matter had a prolonged shoulder. Sublethal injury was not detected under most experimental conditions, and only gram-positive cells treated in distilled water showed a relevant degree of injury. The exposure of bacterial cells to chlorine in distilled water caused extensive permeabilization of the cytoplasmic membrane, but the concentrations required were much higher than those needed to inactivate cells. Therefore, there was no relationship between the occurrence of membrane permeabilization and cell death. The addition of organic matter to the treatment medium stabilized the cytoplasmic membrane against permeabilization in both the gram-positive and gram-negative bacteria investigated. Exposure of E. coli cells to the outer membrane-permeabilizing agent EDTA increased their sensitivity to chlorine and caused the shoulders in the survival curves to disappear. Based on these observations, we propose that bacterial envelopes could play a role in cell inactivation by modulating the access of chlorine to the key targets within the cell.
Article
Growing attention has been paid to the dissemination of antibiotic resistance genes (ARGs) in wastewater microbial communities. However, the disinfection processes, as microbial control technologies, have not been evaluated for their impacts on ARGs transfer. In this study, the effects of ultraviolet (UV) disinfection and chlorination on the frequency of ARGs transfer have been explored based on the conjugative transfer model between gram-negative strains of E.coli. The results indicated that UV disinfection and chlorination exhibit distinct influences on the conjugative transfer. Low UV doses (up to 8 mJ/cm2) had little influence on the frequency of conjugative transfer, and UV exposure only decreased the bacterial number but did not change the cell permeability. By comparison, low chlorine doses (up to 40 mg Cl min/L) significantly promoted the frequency of conjugative transfer by 2~5-fold. The generated chloramine stimulated the bacteria and improved the cell permeability. More pilus were induced on the surface of conjugative cells, which acted as pathways for ARGs transfer. The frequency of ARG transfers was greatly suppressed by high doses of UV (> 10 mJ/cm2) or chlorine (> 80 mg Cl min/L).
Article
The occurrence of a viable but nonculturable (VBNC) state in bacteria may dramatically underestimate the health risks associated with drinking water. Therefore, the potential for UV treatment to induce a VBNC state in Escherichia coli and Pseudomonas aeruginosa was investigated. UV disinfection effectively reduced the culturability of E. coli and P. aeruginosa, with the destruction of nucleic acids demonstrated using gadA long gene fragment qPCR amplification. Following UV radiation, copy numbers for the high transcriptional levels of the 16S rRNA gene varied insignificantly in both strains, confirming results from plate counting assays indicating that VBNC states were induced in both strains. Furthermore, the virulence genes gadA and oprL remained highly expressed, suggesting that the VBNC bacteria still displayed pathogenicity. Propidium monoazide qPCR indicated that cell membranes remained intact even at a UV dose of 300 mJ/cm2. The RT-qPCR results after UV and chlorine treatments in E. coli were significantly different (8.41 and 5.59 log units, respectively), further confirming the induction of VBNC bacteria induced by UV radiation. Finally, resuscitation was achieved, with E. coli showing greater resuscitation ability than P. aeruginosa. These results systematically revealed the potential health risks of UV disinfection and strongly suggest a combined disinfection strategy.
Article
Bacterial antibiotic resistance (BAR) in drinking water has become a global problem considering its public health risks. Usually the antibiotic concentrations in drinking water are too low to select the antibiotic resistant strains effectively, which indicates factors other than antibiotics would contribute to the emergence of BAR. The effects of mutagenic disinfection by-products (DBPs) on BAR were investigated. Four typical DBPs, dibromoacetic acid (DBAA), dichloroacetonitrile (DCAN), potassium bromate (KBrO3) and 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) were chosen. After exposure to DBPs, the resistances to ten antibiotics were raised by various levels, norfloxacin and polymycin B resistances were enhanced even more than tenfold compared with control. MX increased the resistance most observably in the selected DBPs, which was consistent with its mutagenic activity. Multidrug resistance was also demonstrated. And the resistant mutants showed rather stable during 5-day culturing. The BAR increase induced by DBPs was due to mutation since the ROS formation was quenched by adding hydroxyl radical scavenger. Sequencing of the related genes further confirmed the occurrence of mutagenesis. Our study indicated the mutagenic activity of the selected DBPs could induce antibiotic resistance, even multidrug resistance, which may explain partially the lacking agreement between BAR and antibiotic levels in drinking water.